Yep, great amps, which is the reason i say buy an original. Should be able to get one cheaper than a brand new 6505+, i also believe the new ones are not built in the US were as the originals are, and from my own ears, I'm convinced the originals sound superior to the 6505 range.
If it were me, i would certainly have a US built head for less money. The sound thing is subjective. If you have a clear enough memory of the 5150 II then i would try a 6505+ and see if it pushes the same buttons as the 5150. The 6505 did not for me, but if it does for you, go for it.
BTW, am absolutely not saying the 6505 is a bad amp, it's not, am saying i prefer the original 5150 to it and usually, in the uk and states, it's cheaper.