I have yet to see a graph of a 6765 spooling faster than my s372....it spools faster than my 57 trim did. The only reason I'd go smaller is to run in a less expensive class. I wish I had a picture of the graph. I am going to try to make a boost leak tester and put some more springs in the wastegates and go at it again.
I had a 372 and went to a 6765. The 6765 made more power until 6-6.5k and after that the 372 took over made alot more power. The difference in spool wasnt as big of a difference as i thought it was going to be, and i had a smaller turbine housing on the 6765(.68 on the 6765 vs. 1.10 on the 372). It was all precison had in stock at the time. Overall i was very disappointed with the 6765. I sold it less than a week after i bought it.
We dont race our from 4-6k, so who cares. The 6765 felt alot more responsive on the street, though. You could drive kinda lazy with it, and shift easy and full boost would be there. Gotta bang the gears to keep full boost on the 372.
The only reason to go to the 6765 would be if you were running a 67mm class, and at that point a 6768 is going to be the best choice.
(i had wrote alot more but it didnt send and got lost.if you want more details pm me)