Black OPS is no mean feat for a GPU. It puts many big cards to shame! Its quite badly coded and does have its issues with FPS.
Look at this:http://www.techspot.com/review/346-gigabyte-geforce-gtx-570/page5.html
Test System Used:
- Intel Core i7 920 (Overclocked @ 3.70GHz)
- x3 2GB G.Skill DDR3 PC3-12800 (CAS 9-9-9-24)
- Asus P6T Deluxe (Intel X58)
- OCZ GameXStream (700W)
- Seagate 500GB 7200-RPM (Serial ATA300)
GTS450 gets 26 FPS. Now with that in mind, i would say it was a miracle that you got 30FPS in the first shot.
5FPS - 10FPS is just about right for a GT220.
Oh... one more thing, Also what resolution are you playing at?