Touring - What's the largest cassette I can use?

If I'm using a compact crank and Ultegra 6600 front and rear derailleurs (short cage), what's the largest cassette I can use?

What if I get a XT M780 rear derailleur? Then what's the largest cassette I can use?

If the XT M780 isn't compatible with road Ultegra 6600, then how about the Deore Shadow M593?

Thanks!

Crap...I just did some reading. Apparently, Shimano 10-speed MTB rear derailleurs don't work with Shimano road groups. But 9-speed MTB rear should work?

So how about the RD M530? The techdoc has a 11-34 min-max cassette...do you think it'll work with a 36t rear?

http://techdocs.shimano.com/media/techdocs/content/cycle/SI/Deore/RD-M530/SI-5VM0B-EN_v1_m56577569830604662.pdf (http://techdocs.shimano.com/media/techdocs/content/cycle/SI/Deore/RD-M530/SI-5VM0B-EN_v1_m56577569830604662.pdf)

Yeah, I am not quite sure on what is happening with Shimano's MTB rear derailleurs right now. I have heard reports of changes in pull, but...

Up until I read that, I adopted Sheldon Brown's approach that all Shimano RDs did exactly the same thing, whether they were nine or 10 speed. That's why I have identical previous generation XT deralleurs on both 10 and 9 speed bikes.

If you have any doubt, look on the internet for NOS XT stuff, if you really want it. I would settle quite happily for LX or plain old Deore, frankly.

Supposedly, the M530 rear is a 1:1 ratio...I'm not sure if that is good or bad though! lol

The largest rear cassette you can use is a 34t. You can use a 36 but need to have a RD that floats. The 9 speed stuff is not compatible with the 10 speed stuff. Lets start with the crank. If its a 10 speed crank then you must use a 10 speed chain and cassette, 9 speed stuff will bind up on the chainrings. If its 9 speed then you are set. The 9 speed stuff is usually cheaper but some stuff like barends is beginning to get slightly difficult to find. If you have 9 speed then a 34t cassette should be functional but not with that Ultegra RD. Short cage is designed for road use and a 28 is about the best you can do with that setup. I would stay away from the M5xxx series as I have read alot of poor reviews about it's performance. Jensonusa.com has a handy search feature to help you narrow down your choices.

The largest rear cassette you can use is a 34t. You can use a 36 but need to have a RD that floats. The 9 speed stuff is not compatible with the 10 speed stuff. Lets start with the crank. If its a 10 speed crank then you must use a 10 speed chain and cassette, 9 speed stuff will bind up on the chainrings. If its 9 speed then you are set. The 9 speed stuff is usually cheaper but some stuff like barends is beginning to get slightly difficult to find. If you have 9 speed then a 34t cassette should be functional but not with that Ultegra RD. Short cage is designed for road use and a 28 is about the best you can do with that setup. I would stay away from the M5xxx series as I have read alot of poor reviews about it's performance. Jensonusa.com has a handy search feature to help you narrow down your choices.

Parts of this post don't make sense. The largest cog on a Shimano cassette that is available is a 36. The XT and Deore and M5xx RDs can all handle that if they are long cage. The Ultegra is unlikely to handle anything above 30T because it is mid or short cage in length (if short cage, then even a 30T might be moot).

I use 9sp on 10sp chainrings all the time without issue. And here's the cruncher -- I use a 9sp cassette with 10sp STI shifters. The differences in width on the chain and the pull with road shifters isn't worth worrying about, in my opinion and experience.

As to the durability of the M5xx series, the reviews you've read are likely very minimal and from people who abuse their equipment than touring cyclists. I've not had any issues with Deore level RDs or cranks, nor LX nor XT. But if you ride your bike like you want to destroy it, you probably will have issues.

This is a follow on from this thread http://www.bikeforums.net/showthread.php/843201-Mixing-Shimano-mtb-and-road-components where most of the questions have been answered.

With 10 speed, you can't mix 10 speed road and Dyna-Sys MTB; for RD capacity, from real world experience, an SS will take up to a 30t, a GS will take up to 32t, and an 9 speed Deore M5xx will go fine with a 36t