Thanks for the replies guys.

Tried plugging the monitor into the other card and got the same problem except this time it was with the other card (the one doing 300+ started going at 45 and vice versa) so maybe a dummy plug might be a worth a try.

Started to play with the settings in the config file but got no change to the performance of either card. Going to have more of a play around with the config after work tonight. Will update with results (or none results).