Tevis, 3.55,s or a good vert in your case. Get out there and test your current TCI and see where it stalls at.

As you stated, even you dont know. Do it and report back. If it ends up being around 2400, get a tight 4200 + stall vert and keep your 3.23,s. or keep you TCI and go with the 3.55,s.

Change to the low gear set later, on your 904 rebuild when your ready, as a additional upgrade if needed.