I'm running Middleburn RS-7 cranks on my singlespeed 29er. I've been using a Crank Brothers Cobalt bottom bracket, which just recently started crunching after 4 months of use. I'm thinking about replacing it with an SKF bottom bracket, which seem to be the best quality ISIS bottom brackets out there. I can order either the 300 series or the 600 series from mtbtandems.com (http://mtbtandems.com/SKF.htm). The only difference seems to be the use of stainless steel in the 600 series and coated cro-moly. Is a stainless steel bottom bracket going to last me longer? Any other thoughts?