I suspect you're getting away with a relatively high gear on your 8.5 due to your high start RPM. Temperature isn't bad, and if you don't feel you're hurting on speed anywhere, then it's hard to say you're doing it wrong, but I do think you're probably leaving some acceleration and speed on the table with that gearing.
With any boosted profile, gearing and profiles are very much a personal preference thing, and starting on a profile from scratch takes a lot of testing.
On a large straight track, I would expect to see a car top out before half-straightaway with no boost when geared "correctly", and then make up for loss of acceleration on the rest of the straight with boost. That being said, if the car is geared so light that you can't get traction coming off the corners, going lighter on the gearing also doesn't make a lot of sense.
I prefer a fairly smooth acceleration, no nitro style second gear look to the car, which you have to tune in with your start and end RPM settings.
I haven't run an 8.5 in a TC, but I do remember gearing around 7.1 or so with a boosted 10.5.
Hope that helps.