Re: 6505/5150 4x12 cab any good
Can't speak for the newer 6505 cabs but I play the original 5150 cabs and they're very good for the money. The 5150's are loaded with Sheffields... A little harsher than a Celestion V30 but for hard rock/metal they have a fantastic chunkiness... I also own a Mesa Rectifier cab and a Marshall 1960B w/ Celestion V30's and I'd put the 5150 cab right smack between them tonally.
So for hard/rock & metal I'd say go for it. If you want a smoother, silkier tone for more clean work or light bluesey feel, maybe not the best pick, but still a decent sounding cab. Based on your using a 6505 head though, I'd say it'll rock! I'm using a 1st gen 5150 head with mine and though I mix & match cabs recording, I generally use the 5150 cab for playing out.
For what its worth...