AXIA core's tend to do very good for overclocking if you look at it as an overall percentage rating. I'm running a 1ghz AXIA at 1.4ghz. That's 40% of an improvement over stock. I've seen alot of people with 1.2 ghz chips running around that or a bit higher, but the percentage versus price isn't there. Also, make sure you get a decent cooler for it. When you push 1.2ghz or higher, your talking some serious heat. Go for a Swiftech if you've got the $$, or get a Thermalright SK-6. That's a pretty impressive little heatsink. I'm only pushing about 41C at 1.4ghz.
Hope this helps!