EVH, the company that’s actually Fender but metal guys don’t want to play Fender just like they didn’t want to play Peavey until the 5150, have a limited edition 5150 III now. It’s designated as the 5150 III 100S. It doesn’t sound like a drastic change, just minor EQ and gain tweaks. Both channels are able to coax out a little more distortion. The orange channel is “re-voiced for improved low-mid frequency definition” which is kind of ambiguous. Maybe the knob adjusts a different frequency. I’d love to get a more scientific explanation. As for the red channel, it’s low knob has more range.
The final EQ tweak is the one I’m most excited about though: the return of the resonance knob. Peavey 5150 users will be familiar with the resonance (what most other amps refer to as depth) and presence controls, which were in the chain after the preamp so they could give you some extreme low and high boosts. But the 5150 III ditched the resonance control in favor of three separate presence controls: one for each channel. Now that resonance is back it’s also on all three channesl, with the knobs on the rear panel, so it’s more versatile than on the old Peavey 5150s and current 6505s.
One last thing: most users agree that the 5150 III’s orange channel is actually a little bigger sounding than the red one (just like how the clean channel on a Peavey 5150 with the crunch button engaged sounds meaner than the distortion channel), but it didn’t have quite enough gain for metal. If the boosted gain on this limited edition crosses the border into metal territory than that alone would be worth the extra $400 that the S sells for.