On paper, the PF800 is similar to the RPM.
Bass is at 40 Hz, Sansamp at 80 Hz.
Mids at 220,450,800,1.6, 3 KHz, Sansamp (RPM) variable from 170~3KHz
Highs at 4 KHz, Sansamp at 3 KHz
If you are really looking for emulating the Ampeg tone, also consider the Sansamp VT Rackmount.
I use the RPM+VTRM with a solid state power amp.
PF800 is a head, and not a drop-in for a conventional rack.
Sansamps are intended for rack mounting, and will use a rack mountable power amp.
PF800 at 11.8 pounds weighs a lot less than two Sansamps, a power amp, and rack case.
PF800 is 400w into an 8 ohm load. Is this enough juice?
My Sansamps drive a PLX-3002 or ProLite2, both which are 3KW amps.
Q: is this a live performance rig, or heavy use in recording?
The Sansamps offer a lot more variety in tones, which will be lost in live performance.
Unless you are knob twiddler, you will probably use one Mix and one Solo tone for use in a live band.
A pair of Sansamps can be switched between units with a floor switch.
My RPM is set up for fat and punchy, and the VTRM set for a solo heavy grind.
When I die, I hope my wife does not sell all my toys for what I said I paid for them...