The Sanden SD508 unit on 2511 is Sanden model U-8390. It has a 5.2" diameter pulley.
The Pantera OEM cast crank pulley is 5.5" in diameter.
With the diameters being so close, you can figure your compressor RPM will be just a bit faster than engine RPM.
Engine rpm 3500 = 3700 compressor rpm
4000 = 4230
4500 = 4760
5000 = 5290
Larry