Hmm... when does it become unbearable? when you have 500+ units slugging it out??
My Computer (referenced earlier by Calum :p ) is Very Good up about 750+ units, but it is still playable.
It is probably a resolution problem... but maybe its a actual game instillation problem, as referenced on Gas Powered Games Forums. i would link to it but i forgot the location
apparently if there was a problem/power surge during install or if the DVD-drive had a problem, or any of a hundred of hardware problems... it would not correctly install one of the engine files and it would fail too hold up under stress apparently...
But that is a rare problem. i would have a better look at your system... i personally think a totally over clocked system would never ever hold up very well under a high processor Dependant game, maybe RAM also needs upgrading.
that and i don't think pure over clocking is good for a system IMO.
please get back to us if you fix it