I'm no guru but I'll give my experience
ok general vendors say TA49s @545HP Need 2600-2800 stall to be happy, the TE44s @580HP also require the same 26-2800 stall to be happy. I say "happy" because when my stock turbo blew its seals, I had installed an ATR Stage II turbo and with the stock converter felt a little sluggish off the line. It wasnt til after THAT turbo started smoking that I went to ask Jim Haas for help and he hooked me up with a polished TA49 and the car was Still a little lazy off the line. that same week I bought a Kenne Bell 9/11 3500 stall converter to solve my lag woes once and for all! IMMEDIATELY there was a night and day difference! (Very Happy Turbo) Even with a front mount intercooler, 2 3/4 up pipe, and 70mm TB...the boost guage would climb as fast as if it were an RPM tach when reved! Besides, if you went to a reputable 3500 converter you'd be prepared for the bigger turbos when the urge hits. and arent 9 inch conerters the norm and easy to find? HTH