IIB has a very loose low end that gets a bit too flubby for high gain metal tones IMO.
I mean don't get me wrong, you can cop some great old school/classic metal tones, but it just doesn't have the tightness or quick response the c+ has. The c+ has more gain on tap, and very solid low end that gets you that "Hetfield God Sound" as Bob Rock put it.
The IIB has amazing clean, and early break up tones, that you can pretty much get on a c+ with different settings.
Mike b's loop mod, if you can afford it, makes that amp have the tight low end of the c+, but still the milder gain thickness of the IIB, giving it a unique sound all its own. i'd love to have another one of those one day.
IIb is more common, as way more were made, so that also keeps it in a realistic price range, although they certainly have bumped up in value 3 or 4 hundred in the last 10 years. When i was flipping gear in the mid 2000's those could be obtained for 500 to 850 max for a nice loaded one. maybe a grand if it was hard wood. Now, unless they're in some ugly ass cabinet or hacked up, they start around 800 used.
c+'s have jumped about a grand, easily in the last 10 years.
edit: someone got a steal right here:
https://www.ebay.com/itm/Mesa-Boogie-Ma ... Sw6zNbhjSr