I've listened to the 6500s in 3 different vehicles, including my own every day. IMO, they are very nice speakers for their respective price range. The only complaint I, and others have about the 6500s is the lack of tight/snappy midbass at lower power levels. When running with less than 150 rms a side, the midbass is slightly lacking, even with tons of deadening, and properly sealed door etc.
If you give them enough power, they sound just as good, if not better in the midbass area than the seas lotus performance comps I've heard. And that's saying something. My roommate is feeding his 6500s about 175ish rms/channel, and his absolutely pound. You can turn the subwoofer off, and the system really doesn't sound much different. Still full and punchy.