since I haven't seen a pic of one here, thought I share my Colnago Classic. (nb: that's not a Classic Colnago, but the other way 'round.) This is my first road bike, purchased 2 years ago after my second back surgery made me rethink mtb'ing on the regular. I've been steadily upgrading since its initial incarnation w/a full Centaur gruppo.
Here's my question: This is a 56cm. I'm getting ready to take the plunge (and thoroughly piss off my wife) by ordering a C50. I'm considering the 52cm sloping which should keep the top tube virtually the same, but allow me to show more seatpost (which I want b/c I want more setback, and am leaning towards a Thompson setback post.)
I'm curious if anyone a) sees any flaws in my reasoning or b) has experience with fitting on sloping v. non-sloping Colnagos.
As a bonus question: I weigh 180 lbs., ride some pretty crappy roads around Sonoma/ Marin in NorCal, and have the aforementioned back issues. Would a C40 be kinder to my back and/or would a Force (vs. Star) fork be plusher? I'm not racing but do ride around 150 mi./week with 5-10,000 feet of climbing.
thanks in advance for your collective wit and wisdom,
peter

Much as I love my C50, the C40 would probably be a better ride for you -- not as harsh while still being very stiff in the good ways. Think about some carbon bars, too -- not the oversize ones.
I set up a bike this way for a friend, using the Fizik Aliante saddle, and it has worked for about 2000 km so far without his previous pain from various back problems and surgeries

if you get a C50, definitely get the Force fork -- the Star/C50 combo is VERY stiff.

Just a comment on the Thomson set back post, it's deceiving because it really does not move the post back. A regular Thomson puts the seat directly over the center of the post, so the set back Thomson puts a the seat back where most traditional posts put it. But a Thomson set back is not really a set back post... it's more like a traditional post and the regular Thomson is a very forward post.

If you want a post with a lot of set back, I would suggest a Moots set back post or something from Easton. Even the Campy posts have quite a bit of set back.