All of the 226's are mechanically the same / with the exception of some trigger options...
I have a pair of 226's , all stainless, one in 9mm and one in .40 ...both very good guns ...several thousand rounds thru each of them with no issues.
http://thefiringline.com/forums/atta...1&d=1344296606
The mk 25 is only cosmetically different - with the anchor on the left side of the slide...which is kind of cool / if that's what you want.