e-tailers rarely even know the stepping they carry. The only way to know for sure is to remove the
HSF and look directly on the CPU for it. I've had or helped build w/ 3 AGKGA durons, none wanted to go over 1ghz. I was using good air cooling and 1.85v. I also got very little extra speed for the extra voltage. Going from 1.6v to 1.85v only allowed another 50mhz or so.
If you don't want to spend extra, try upping the fsb without touching voltage. Depending on stepping, you might get to 1gig with low voltage, and less heat. Just keep an eye on your temps. At least see what your chip is capable of. You might be happy with the simplest and easiest o/c.