Generally with the Trek range, the higher model you get, the better parts you are getting for your buck. Its a good system, you just get the best Trek you can afford.

If it is possible to test ride these bikes, whether they all be at the same store or not, go for it. I wouldn't settle for the '06 Trek police bike if you think its a little cramped...in fact don't settle for a bike if it doesn't fit you.

The 6500 is a nice bike, and the '08's are really nice. Just get out an test ride some.