I don't know which turbo would be best. I want to make 250-300whp.
Is the K26 bigger than the .60/.63?
Would boost start to drop off in the upper RPMs with the .60/.48 T3?

Has anyone used the K26 or smaller T3 above on a B series?

 

Sounds like you need to start reading some compressor maps and plotting points. That will tell you everything you need to know and will be much more accurate over anything else.

 

Do you really have the bottom end to keep up? Do you plan on running stock internals? Research is the key to success here.

 

on a B-series and wanting to make 250 hp I would go with a .60/.63
Plus the T3's can be easily upgraded to T3/T4's...

 

Where could I get the maps for these turbos though?

B series internals can handle 300whp. There are quite a few cars making that power and more on stock pistons etc.

I'd love to get the .60/.63 but they're hard to find.