A great article about CPU scaling with a HD 4870x2 here http://www.legionhardware.com/document.php?id=770
What I'd like to see are CPU scaling articles with mainstream GPU's like the 4670, 4850 and 4870. We know that the higher numbered cards give the best overall performance, but that can change depending on resolution. Anandtech's article on the 4670 shows they were impressed, with the caveat that beyond 1280x1024 without AA the 4670 sometimes is beaten by a 3850 and always by a 3870; let alone the better cards in the 4xxx series.
The 4870x2 could run into CPU limitations with a Q6600 at less than 1920 resolutions, and it seems to be a bit limited until 30" LCD resolutions are reached. IMHO, each GPU by ATI and Nvidia should include recommended CPU's from AMD and Intel with preferred resolutions, but I'm sure both companies don't mind selling high end cards to anyone who has the money, regardless of what CPU and resolution he games at.
Can't wait till I'm no longer CPU limited (next upgrade soon!). My recommendation for anyone building is to focus on matching your GPU to the right CPU and resolution. It's not as good buying a better GPU than you need with the hopes that you'll upgrade the rest later. If I'd not been wowed by 3870x2 performance, I'd have saved money with a 3850 and then achieved 3870x2 performance later on with a sub $200 part when I finally had the CPU and monitor to match.
I'm gaming with the PC in my sig plus a 17" Viewsonic CRT at 1280 x 1024 (which limits the 3870x2 big time).