Go above the 38T rear sprocket and you'll need a longer chain. You may get away with a 39T, but probably wouldn't notice any difference??
I've geared mine down to a 36T rear and ride the mid range. It'll still rev to the limiter in 5th though, and that's reset to 11500rpm
I ran a 42T rear and it hit the limiter in top at about 150mph or so. Too buzzy for me though, hence the lower gearing I now run.
For the turn in, the ride height is probably on the stock setting? Put two full turns of the tie rod into it and it'll turn on a sixpence.