I did not notice the game playing any differently, but I must confess I have not looked at the FPS display either.
I wasn't planning on spending any money on upgrading, the game ran "good enough" already. Then almost by accident I ran across a 2 gig processor and motherboard combo on ebay for a little over a 100 bucks brand new in box. Ebay has some great deals, I know it can be time consuming and risky but worked out for me (this time).