I also recently found an oddity that might explain this. I recently got a new GPU (Gigabyte GeForce GTS450, 1GB GDDR5, not overclocked) and I get a similar performance drop. I notice that the new card doesn't even get warm while playing Eastern Front, but playing vCoH or any other game is fine (card gets hot but performance is good).
Could it be that somehow EF does not recognise this card or is somehow prevented from using it?