Did a search and I can't seem to find much technical data, mostly marketing speak, on the mechanical differences between the Ultegra and 105 short cage rear derailleurs. I see from the Shimano tech document that the Ultegra can handle up to a 28 tooth cog and have found sales descriptions for the 105 claiming 30. Currently running a 12-27 9 speed cassette, so both should work and the chain wrap requirements claimed for both are good also.

Just wondering if anybody knows what real differences there are between the two; such as bearings vs. bushings, metallurgy and the like. Finish is of no matter...don't look at my rear derailleur when ridding anyway.