I have a 5150-II (same as the 6505+). The cleans are not great, let's get that said. But the distortion is brutal, can be made exceedingly tight, and this amp really, really kicks high-gain buttski. I would recommend trying one out first, though ;) Also, the cab makes a big difference. The 5150 cab is okay, but not amazing. I swapped out the speakers in my 5150 cab and that has made it even more brutal, but I'm sure a better made cab would make things *even better*!
You might also want to consider other amps like the Bogner Uberschall and the Rivera Knucklehead. I've not got experience of these, but I have heard good things on these forums...
Roo