I would aim for as high as possible. You may find it entertaining like many do to find your highest clockspeed then compare it with others. For 24/7 running, load temps should not exceed 80c.
If your just going for a High speed screenshot then you can go all the way up to 80c idle, if your voltages arnt to dangerous at that point.
Killer system you got there, now go in and overclock!
When you get a personel best, make sure to submit it to me in this thread, thanks:http://www.tomshardware.com/forum/256708-29-core-overclocking-club#t1837694