Shimano, though they say that their objective with the M770 redesign of Deore XT was to increase durability, they also did some serious dieting for their rear derailleurs. The Shimano Deore XT RD-M771 Top Normal Rear Derailleur is 26g lighter this year, and is supposed to be more durable to boot. So booting it isn't as much of an issue. While you won't catch anyone at Shimano telling you to abuse this derailleur more, they did design it with that in mind.

Top-normal means the spring tension in the derailleur pushes the cog down to the smaller or harder cogs. Aka "traditional," this is the one you grew up with. While it is designed specifically to work with the XT Rapidfire Plus, but will work with Rapidfire, SRAM 2:1 shifters, and in reverse on Shimano DCL (down is up, up is down).

The Shimano Deore XT RD-M771 Top Normal rear derailleur is offered in two sizes: GS (mid-cage) and SGS (long-cage). In all cases, the max cogset that can be used is an 11-34. The difference is that the mid cage size has a 33 tooth total capacity while the long cage takes 45 tooth total. All XT rear derailleurs have sealed 11-tooth upper and lower jockey wheels. The spring in the derailleur yields Shimano's traditional "light action" gear changes. 239g (long cage). MSRP $109.99.