Quick update then. Had camera set to centre weighted, IS off, light was bad tonight so had to crank up the ISO to even get remotely near to F8 (best I could get was 5.6 @ ISO1000) still only giving a slowish shutter speed.
Tried reducing the extent of the zoom to around 300 / 350 to open up the aperture a bit ( bit of an improvement, but obviously need to get closer still to subject).
All charged up, ready to go, remembered to load CF card!!!(Done that before ha ha).
Couldn't really take Benbo Tripod as the location is just a huge marsh, and the birds don't yet have a distinctive flight /hunting pattern, so I need to hand hold shots (May invest in a monopod tho')
Yep - One bird turned up, but was so sporadic - was all over the place, and didn't stay long enough, so couldn't test everyones recommendations out, then it started to rain.
Oh well, Sods law & all that. 
Will keep visiting as long as they keep coming.
One day I'll get that pic!
Thanks all for the advice / tips etc.
