I had a 5150 mkI head back in the day (was never a metal guy, was more Smashing Pumpkins kind of thing at the time). I loved that amp, went from Who-esque classic rock to meltdown and cleaned up beautifully with the volume control. Never found it too harsh, too bright, too fizzy. But, like Robbie61, I ran it through a Marshall 4x12. The first time I played one through it's own Peavey cab I got a shock. The bees! The bees! The Marshall cab really seemed to round it out and take the edge off.