smaller rear exhaust housing will allow much faster spool up, being a relatively large turbo. My suggestion is to go with a IHI/Apexi AX6 turbo, im running one on my 33 RB27DET and its awesome, spools up early full boost easily by 4 or less and cranks till 9,000rpm or more its a fun turbo to have and u wouldnt regret it, but same thing applies, a smaller rear exhaust housing and itl b crazy..mines larger but i got heaps of engine work