Can anyone offer any advice on this? Are the above values safe to use without permanently damaging the unit's clock generation in some way?
I've used 100 MHash/s steps a lot for testing/fine tuning individual ants. No harm done. 
It is quite comfortable but has one astonishing problem... it only accepts multiples of 25
I wanted to try frequencies like the earlier reported 262.50mhz but that's a no go.
Version 4.0 of cgminer allows any arbitrary frequency at all from 150 to 500 and it will try to find the nearest frequency that it can try to set the device to.