Far cry 2 framerates

I have upgraded my system which was an Amd x2 5000+, Asus hdmi board and single 512mb HD4870 card and 4gb ocz reaper ram to
The following spec. Old system played farcry2 very playable on high settings with 2x anti alias. The new system manages 20fps max with all settings on ultra high and 8x anti alias and reducing to high settings and 2x anti alias i can get 30-50fps is this normal i expected my system to eat the game for breakfast but clearly it seems only a very few of the most powerful systems on the planet will play this game maxed out. Just for reference i play Call of duty world at war at 91fps with everything maxed out at 1490x 900

Amd Phenom x4 9950 2.6ghz Black edition (oc to 2.8ghz)
Msi Platinum K9A2 M/board
4gb Ocz Reaper 1066
2 x HD4870's 512mb in crossfire mode
850w psu
160gb Maxtor hd (sata)
500 gb Maxtor hd (sata)
Windows Vista 32 Ultimate
Acer 19" Lcd Monitor (1440x900)Max res