I recently did just that, got rid of my 6505+ and got a caliber 50+. I wouldn't do a straight trade though since I sold my 6505+ for $800 and bought the Caliber 50+ for $400 (it needed tubes and the jacks cleaned, they go for about $500-600 in perfect shape)
It is less brutal then the 6505+ but make no mistake, it still PLENTY of gain for any style including metal, it's jut more of an old-school metal tone (old Metallica, COC etc...) while the 6505+ sounds more modern. But the Caliber sounds more musical and is much more versatile and better built than the 6505+. It's simply a better amp IMHO.
I am very happy with it.