ATI Radeon HD 4890 very low FPS Left 4 Dead

Okay, so I bought this card off of Newegg expecting to be able to run pretty much everything on max settings without any problem, and thats what all of the benchmarks indicate when you go look at them. Now, heres the thing though, I am in the middle of building a system and so far all i have bought is the GPU, Case, PSU and HDD so I am still using a two year old motherboard (ASUS NARRA2 nForce) with an Athlon 64 x2 4000+.

Now my question is, does bitching card + crappy CPU = epic fail?

I am truely confused because i can run Mirrors Edge on maximum settings (no Physx obviously) no sweat, runs around 50 to 60 FPS the whole game, and I can pull crysis on all high with x4 AA and still get 20ish FPS, which is what i am getting in Left 4 Dead. A nearly six year old engine should not need the same power as, well, crysis. I run CoD 4 and 5 60 FPS stable the whole time. Could it be the combination of a nForce mobo with an ATI card? Or is it truly just the fact that my CPU has aged?

P.S. I know some people had problems with the AA in Left 4 Dead and I disabled it but i get the exact same FPS. Also, this isn't single player so its not that my computer has to control the director and all the zombies as well, online play. Its also interesting to note that Garry's Mod gets stable 60 FPS for me.

my temps are fine, idles at 40, underload its around 55 to 65, how should i go about OCing my CPU? my BIOS is pretty crappy (AwardBIOS) and it doesnt have any advanced options..

oh wow thanks. how much higher should i clock it? just a tad each time and see what happens? I have an Antec 1200 so cooling wouldnt be too hard to compensate for.


EDIT: meh... i get an error when i start the program, "AMD OverDrive cannot detect AMD 7-series chipset on this computer." will google around to see if theres anything i can do to fix this but.. seems like ill just have to live with shitty graphics on left 4 dead until i can nab up a motherboard and a CPU.. Any suggestions as to what CPU i should get so that i can avoid this issue in the future? i plan on using crossfire for a second 4890 in the future if that changes anything.

The source engine is more CPU dependent then most newer games. I'm thinking CPU bottleneck.

well, the problem is that my motherboard is a stupid HP mod of ASUS NARRA2, but im going to download dosbox and hack my bios to manually unlock the options (software guy here, very obviously not a hardware ) and then ill just do a nice little OC. Thanks for all the help guys