I think anything over 2.5" is just silly unless you're running a GT and can actually use it. Necking it down to fit on the K04 isn't helping your flow at all IMO and the transitions from smaller 2.6 MAF to larger 3" inlet then back again to smaller 2" adapter are just not desireable in my mind. I think 2.25 would be my choice followed by 2.5 and anything larger, I wouldn't buy.
In retrospect, the only unit available at 2.25 is the CS which you can't buy alone AFAIK. So it's Cobb, or HTP or as others have done, weld one up yourself I suppose.
