I have used the PF500 with an Ampeg SVT410HE for mainly classic rock, funk and blues the last couple of years and are very happy with that, sounds really good and no problems at all. I mainly use a Mexico P and a USA G&L 2500.
I am a project manager for a company which delivers electromechanical equipment (turbines, generators, control and governing systems, valves etc) for small hydropower plants from 200 kW to 10 MW