I now have acquired 4 bikes that are all capable of being ridden without fear of mechanical breakdown or having to borrow parts from each other to make them rideable. I have taken a few months off from any regulated training and recently began a normal riding schedule. The first thing I noticed was that 2 of my bikes felt different as in saddle height felt way off on one. So I measured and the saddle heights were different and i measured the other 2 and they were different also. Now normally I am fairly meticulous about setup using a lockable tape measure to measure things out. The question I have is considering that the geometries are a little different on all 4 bikes and I have saddle fore and aft dialed in shouldn't height be about the same for all 4? I'm mainly concerned with top tube length when considering a frame which is why I'm thinking all 4 should be same.

Never had 4 bikes or given a thought to the problem before, multiple bike owners chime in with your experience. What I am trying to do is reduce the risk of some type of knee or hip pain from being way off and riding different bikes on differnet days. I'm thinking each bike will ride a bit differently but saddle heights should not be a noticeable difference.

now i only really ride one bike (no space to keep several anymore), but when i had a few different bikes i had the same saddle height and setback from BB on all of them, reagardless of the crank length (most were 175 but a couple were 170). this was the same for all my road bikes (race and touring bikes). on the MTBs I usually set the saddle 5mm lower than on the road bikes.
before, i had the same model of saddle on all my bikes (a rolls). now I have an arione on my road bike, and initially set the saddle tip to the same setback as with the rolls, but have had to move it forward slightly beacause the arione is longer than other saddles and i found myself sitting too far forward on it to be comfortable with the old setback.
the simple answer to your question would be yes - use the same saddle height and setback on all your bikes.

foz

Assuming you use the same saddle on all, measure the setback by plumb-bob. Mark the distance from the BB to saddle tip on a piece of masking tape on the top tube and measure them. Can also be done on the chainstay. Re-check saddle height after making any fore-aft adjustments.

I have experienced similar feelings over the years and have put it down to the individual idiosyncrasies of individual frames. I currently have seven bikes and the saddle heights and almost identical (as close as they can be), they all have Fizik Ariones on them and all the stem lengths are the same. The saddle fore/aft positions are also similar and so one would think that given the dimension are to all intents an purposes identical, that the bikes would feel the same. Not so. My Casati is still as laid back and solid as ever, my De Rosa feels a bit nervous and I haven't made up my mind about my Argon 18 yet – it’s a lovely ride but I can't categorise it yet. My Specialized frames don’t even warrant a mention.
You didn’t mention wheelbase, fork rake and trail, and head and seat tube angles. That plays a big part in terms of bike feel even though the bikes my be similar in terms of size and set up. Sorry I can't help more but I'm in the same boat as you.

The most critical part of setting up multiple bikes to fit the same is to have the same saddle on all of them. If you don't, then "saddle height" is just a rough measurement, since no two saddles sit the same. The setback measurement would be even less meaningful, unless you take an accurate KOP measurement on each bike. KOP measurements are tough to make accuarately, unless you mount each bike on a trainer and actually ride it for awhile to be sure youre sitting in your normal riding position. Of coures, the bikes have to be leveled while on the trainer, or a plumb bob won't be of value.

I have two bikes that have the same saddle. To insure more precision, I take a measurement from the center of the crank to the lower edge of the saddle, a specific distance from the nose. This eliminates errors that would occur if I measured along the center of the seat tube on these two frame with substantially different STAs.

Once the saddles are adjust to have the same setback and height, then simple measurements from the the saddle tip to the center of the bars, verifies the same reach, since I also use the same handlebars. In different bars are used, then a more meaningful comparison of reach would require spanning between the brake hoods with a 1" dowel rod and taking a measurement from the saddle tip to the inside of the rod. This measurement accounts for the difference in handlebar reach and brake hood placement.

I now have acquired 4 bikes that are all capable of being ridden without fear of mechanical breakdown or having to borrow parts from each other to make them rideable. I have taken a few months off from any regulated training and recently began a normal riding schedule. The first thing I noticed was that 2 of my bikes felt different as in saddle height felt way off on one. So I measured and the saddle heights were different and i measured the other 2 and they were different also. Now normally I am fairly meticulous about setup using a lockable tape measure to measure things out. The question I have is considering that the geometries are a little different on all 4 bikes and I have saddle fore and aft dialed in shouldn't height be about the same for all 4? I'm mainly concerned with top tube length when considering a frame which is why I'm thinking all 4 should be same.

Never had 4 bikes or given a thought to the problem before, multiple bike owners chime in with your experience. What I am trying to do is reduce the risk of some type of knee or hip pain from being way off and riding different bikes on differnet days. I'm thinking each bike will ride a bit differently but saddle heights should not be a noticeable difference.

C40 has it correct, if you want to be in the same position on each bike you should use the same saddle and set it in the same place relative to the BB on each bike. Then adjust bar height and reach to match. You also need to be using the same pedals and shoes on each bike.

Warning: if you are really sensitive to this stuff you run the risk of becoming obsessive-compulsive about your setup. This can actually start to be very counter-productive, where instead of riding you spend more time fussing about. And for some guys bike position and setup even becomes a "crutch". Bad day on the bike = change in saddle position for some!! I'm not kidding. For me, I find that as long as I get the saddle in the right place relative to the BB on all my bikes, and get the reach/drop within a 1 cm range then I'm pretty happy.

I also think how I "feel" on the bike from day to day is probably more a function of my off-bike habits. Time spent sitting at desk, time spent standing/walking, sleep, stretching or lack of it, etc, etc.