GTX 570/580 Upgrade - Upgrade CPU & Mobo or no?

[PredatoryLizard]

Planning to upgrade my rig for the new wave of games coming out. I am definitely going Nvidia 570 or 580. What I am wondering, is should I upgrade the CPU & motherboard as well, or will my current rig be enough to get the most out the card and the new games.

Current rig:

Phenom II X4 945 OCed to 3.8GHz
4 gigs RAM
2x HD 4890s in crossfire
MSI 790GX chipset motherboard

I am debating upgrading to an LGA 1155 system, new mobo and i5 2500K (I'd OC it of course). Like I said the graphics are definitely getting upgraded, and my question for the forums is will I see a noticeable difference if I upgrade the CPU & mobo alongside the new graphics card, or will the upgrade be so slight I should invest that into other parts (a nice SSD, 2x 570 for SLI, etc)? I only worry about some weird issue with the 790GX chipset or the current Phenom CPU not fully utilizing the 570/580, could that pose any issue?

 

[kajabla]

You'll certainly need a better CPU if you go 580, and the 570 will run fairly slow as well. This will not do.

 

[Why_Me]

http://www.anandtech.com/bench/Product/88?vs=288 <----- AMD Phenom II X4 955 vs Intel Core i5 2500K

 

[kajabla]

^I mean yes, but that doesn't really answer the question.

 

[Sky03]

Okay this may sound dumb but, isn't 2 4890s in crossfire competitive against the gtx570/580 (single card)?

 

[kajabla]

Seems like it should be, yes. Can you check what kind of CPU usage you get in games?

 

[PredatoryLizard]

My G13 gamepad has a CPU/mem monitor that i glance at occasionally, sometimes 1 or 2 cores spike to near 100% but mostly its 40-60% or so (in Rift for example). But that doesn't mean I won't benefit from the cpu/mobo upgrade right?

Where did you guys see any comparison between the 2x 4890s and a single 570/580? I can't find any direct comparison worthwhile maybe my google-fu is weak i dunno. Since 4890s are dx10 and 570/580 dx11 most charts i see don't show the two side by side. I saw some single vs single but not cf 4890 vs single 570/580.

 

[kajabla]

I haven't seen a direct comparison; I'm just inferring from the Tom's hierarchy chart. I hadn't considered the DX10 thing, though.

 

[PredatoryLizard]

OK well thanks all, I'm gonna go ahead and splurge for the whole upgrade, I'll be waiting till closer to Christmas and hope the 580s drop price!