I had the same problem. Every ROM that I tried was the same. And when I returned to stock ROM, same thing happend.
When I first returned to stock, everything was ok. But, after CM10, stock is a piece of crap:) So I RESTORED back CM10, reboots started. I went back to the stock and reboots happend even then. Then I wiped everything, flashed CM10 (24.2.) and since I flashed it, more then a week now, not a single reboot happend. "Performance" part was not touched, better be safe than sorry:)
Is it kernel thing or hardware thing, I do not know. I don't know how are kernels flashed here since everything is in a ROM. Maybe when we flashed one ROM with bad kernel, that kernel stayed even after we flashed different ROM. I'm not a pro, not a dev, do not take my words seriously:)
When I change ROM-s to Xperia Arc, first I need to flash a kernel, then a ROM.
Can someone here can explain that better, about kernel flashing?