I agree with wapitibob on this one. Vortex HS LR system is another nice one (in addition to the PST), and Vortex does their own custom turrets, like the Leupy CDS, but adds a rotation stop (although not a true zero-stop).
One thing to remember is that, even at 500 yards, your drops can change noticeably with a wide swing in temp or elevation.
Also actual velocities can vary a lot from published factory specs. A good, accurate chronograph is a must, IMO.
Finally, make sure you verify your drops in the field, and practice, practice, practice.