Re: looking for more top end.
If you really don't mind running slower off the line, a set of 2.93s would lower your RPMs at high speed
as far as I know, you are right on the tr3650, I don't know of anyone that changes out the gear ratios in the actual transmission... there are 6 speeds available with lower final drives, however... that can get pricey, a lot pricier than just having the final drive swapped out
2012 IS F Blue IS F Sport
2006 Mustang V6 wannabe