So long as your temperatures and voltages are within reason you can certainly overclock your ram.
1. There will be very little to no noticeable difference in performance between ram at 1333Mhz and 1066Mhz.
2. down-clocking your ram will cause no harm at all, so long as you arn't putting excessive voltage than it requires.
3. Any overclocking has the potential to damage your hardware, if you are careful about what settings you change you should be quite safe overclocking your RAM slightly.
I can't guarantee your RAM will be 100% stable at you desired clock speeds, but it's well within a reasonable goal.