Differences in sound? I've only personally played the XXX.
To me:
Quote by crazy8rgood

In fact, I almost ALWAYS agree with YourDad.

Quote by itchy guitar
One of the best replies ever.

In the same thread

Do you love Arsis?
The 6505/5150 has darker, fizzier, and more polished gain tones.
The XXX has better cleans, brighter, more in your face and crunchy gain tones.
^Yeah, that's pretty much it. From what I've heard from the XXX, 5150's have a lot more low mids.