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.