If any of those reboots and issues you have come from any ICS ROM then this is normal. ICS ROMS will do that to your phone, its not your phone its the ROM. I dont think theres a fix for it if not then itd be implemented already - thats just my guess. It doesnt matter if you underclock or overclock- ICS somtimes gets stuck and will reboot.
Just because some people use ICS as a daily ROM it doesnt mean its the choice for a daily, because its not. (yet) but im one of those that puts up with reboots, freezes and what not so that i can have ICS . I really dont mind all of that, I like ICS
My OV also reboots on ICS roms unless I change CPU frequency to 480 minimum and 600 maximum. I ran Quattrimus ROM for several weeks without any reboots. Sometimes it's difficult to even get to the performance settings before it reboots, so once you get there make sure to check the box "apply on reboot". Mine will only run ICS on those freqs. Try it out and see what happens.