What is the model of Shimano 10s road rear derailleur with highest spring tension, that also fits a 11-32 cassette un-officially (with normal, longer non-Campy derailleur hangers)? I am done with SRAM shifters, and want to run 10 speed Shimano road shifters on my cyclocross bike. One of Shimano's neutral support mechanics at an event earlier this year recommended the Ultegra RD-6700. I have also heard that the 105 RD-5701 has a stronger spring than the previous 5700 version. What about Dura-Ace RD-7900?
Are you running single or double ring? If single any Shimano rear derailleur will fit a 32t rear cassette.
If you cut the chain to the right length*, have an adequate chain keeper** and good dismount technique you'll be fine with any derailleur. I've used a wide variety over the years (with a 28t) with no problems. They do all tend to wear out after maybe 3-4 years.
*You'll want it as short as possible in the 32t. No more links than absolutely necessary.
** I've used a few systems but for the money (and performance) you can't beat a BBG bash guard and N Gear Jump Stop keeper up front. You can Tom Hopper it for extra security if you like. http://cdn.mos.bikeradar.imdserve.com/images/news/2009/12/15/126086...
I used one of these a couple years ago and it worked great even in the mud pits at John Bryan. http://gevenalle.com/product/burd-rear-derailleur/
I've run it with a single ring and a 11-34 in the back. I never pushed its capacity limits while using a double though. On paper a 11-32 with a 44-38 might work. You'd be getting a low tension chain when you get close to the small-small combo though.