The XP2000+ that I got free from AMD will run solid as a rock at 1750 w/default voltage. It will boot just fine at 1800MHz and run windows fine, but a 100% CPU load does crash it at default voltage when running 1800. More voltage stabilizes it at 1800, and I think it could go a little higher, but I'm running it at 1.762GHz for now, at 1.775V, just to be safe. There really isn't much headroom in these. As you can see, we are all topping out at default voltage around 1.75. Mine will actually do 1800 at reasonable voltage, but I think AMD picked out good ones for the giveaway. Anyway, when in doubt, try some more voltage, and a bigger sink. 🙂
Just out of curiousity, what sort of temps are you guys getting? With an Alpha PAL8045 on an Epox 8kha+, running 1.762GHz at 1.775V, I run between 42 and 46C depending on the load (with 46C being the high end under full load). Seems kind of warm, but it runs very stable that way. When I upped the volts to make it stable at 1800, temps went up to 47-48C at full load.
Nack