I got myself into a reboot loop when I had BB 0.7.6 at 1.2Ghz. I caused it by going into Market and clicking "update" on all the apps that had updates available. I was up to about 4 downloading/installing at the same time when the phone just up and rebooted on me. When it came back up, just trying to get into the apps list to change the max frequency in SetCPU caused another reboot. I plugged it in so that profiles would clock it down to 500 then let it sit for awhile, and I was eventually able to set the max speed to be 1000Mhz.
So in case anyone was curious - 1.2Ghz is fun to play with, but not reliable enough to actually use (for me anyway, YMMV)