As we can see from the benchmarks, the AMD Phenom II X4 940 seems like a pretty OK processor for pairing up with the ASRock AOD790GX/128M mainboard. In terms of cost/performance ratio, it is definitely more worth your penny than getting a Core i7 which is faster. In fact, the QX9770 compared is not widely available and cost a bomb.
Of course, you might argue that you could overclock a Intel Quad Core processor to 3GHz. There is no doubt you can do that. IN this test, we are interested in default CLK comparisons, comparing the higher end processors at default clocks.
The AMD Phenom II X4 overclocks by 26% which is a 800MHz from the default 3GHz on AIR COOL. It is reported that this processor can do 6GHz under LN2. Of course, that remains a not practical solution as no one will want to place a LN2 tank at home and run the system for 1 hr per tank other than competing for world records.
In conclusion, this processor should be able to take good advantage of the ASRock AOD790GX/128M as this board opens a lot more opportunities than just using the embedded graphics. You can use Hybrid or even run a proper CrossFire solution on it with 2 ATI cards.