I have a killer hill climb coming up later in the year where my 39-25 won't be enough. (Average of 10% for 11km with many parts above 22% and at altitude. The most painful thing I've done on a bike)

I'm riding shimano 9s road and was thinking about getting an MTB cassette and using a spare MTB rear deralier. But will shimano road shifters work with an MTB rear deralier? I thought I heard something about the throw being different...

Nope, it works fine. I'm running a 9 speed XT mid-cage with 10 speed Ultegra on my cross bike. My brother is running 9 speed Ultegra shifters with a long-cage XT and a 11-32 cassette on his cross bike. Both shift perfectly. The throw (cable pull) is in the shifter. The derailleur only moves as much as the cable (and limit screws) lets it.

You won't have a problem. Just make sure you check your chain length.

You won't have a problem. Just make sure you check your chain length.

Good stuff. Thanks for that!

I used a XT 11-32 cassette and rear derailleur with my Ultegra 9 a few years back on the Death Ride. It worked fine for 15,000 ft of climbing and 125 miles. The engine needed a bit of lube when it was done though.

Don't recall if I had to put a longer chain on or not, but as backinthesaddle suggest you should check it.

Your other option is a compact crank.

No worries at all--my Atlantis' driveline is a complete mix of road and MB parts, and it works fine.