You should try to adjust the voltage settings to see if that helps, but it's possible that you have one of the phones that have little to no overclocking potential.
If you are using JRummy's overclocking app, I would chose 1.2ghz at high voltage. I have tried the low, ultra low and medium voltage. The high voltage is the best to chose from. I have mine set to reboot at 1.2ghz. It is very stable for me. Sometimes I have 1 reboot a day but i think that is the rom I am running.
Here's what I use in jrummy's DX/D2 Overclocking App and the quadrant score I got off of it in RubiX Focused 1.8.6. It's what I found after trial and error which I felt gave me the best mix of speed, battery life, and phone temp.
I only get lock-ups rarely, maybe once every couple of days with a fair amount of use, and they're usually those lock-screen quick reboots that lots of people have been talking about and has been described as a Motorola problem...?
Oh, and experts, let me know if those settings will cause my X to explode in the next couple days...I know the VSELs are low, but it's been running great for about 2 weeks now.
EDIT: higher voltages tend to be more stable, but generate more heat and lower battery life. So when you're doing your trial and error, start high and knock off a bit at a time. And be sure to read the help file with the recommended VSELs for each frequency.