out of several rigs all using the same set-up and configs, this rig is the only one playing up. I'm wonder if I should try a pool server closer to the UK:

Like I said, every now and then there is a bunch of rejects that lead to this rig being banned from drkpool.
I'll fix that, it's a bit sensitive. We had people running scrypt and it was recording all of their shares for 10 minutes before banning them, so I patched the code to be much more quick about it, maybe I overdid it. Thanks
I was going to play around with settings today, but before I started the rejects look much, much better today. Most are at ~0%, some at ~3%. Not sure why yet.
EDIT - add pic and comment on ASICs

Just an opinion - Scrypt ASICs are coming out this summer. A number of players are entering the ring and pre-orders are taking place. GPU miners will be left wondering what to do. Some will multipool, some rent out their rigs, some bounce around looking for something else.
Litecoin has courted ASICs. The active GPU miners wanted a code change, but the devs didn't want to risk changing the code now LTC is so popular, so by default ASIC makers felt secure in investing in ASICs technology.
The GPU miners will end up finding their way to Darkcoin once the difficulty goes up for Litecoin, the price of darkcoin shoots up and there is a liquid market for the coins mined.
If possible, it might be an idea to build in some implied threat to ASICs manufacturers that if they put up risk equity to produce equipment, the landscape may change. This is (1) a deterrent to anyone wanting to find a way to produce ASICs, (2) a long-term commitment to CPU GPU miners and (3) no one would buy an ASIC if there was a possibility that it might be turned into a paperweight.
Litecoin said their scrypt would be ASIC resistant and it isn't. It might not be necessary to do anything for Darkcoin, but then again what's the cost of an implied threat if someone wanted to give it a go?
Just a thought.