Does the Sempron unit have a discrete video card? The Windows Index will report the score for each category and if the lowest score is for graphics, then it means that the graphics capability is the least weakest point for that system.
The lowest Phenom II setup subscore was 3.5 for graphics. The memory score 3.9 and 6.7 for processor @3.5Mhz. Unlocked to quad the processor score jumps to 7.4. Both setups are using the HD 4200 onboard. Neither has a discrete video card.
The sempron setup 4.7 graphics 5.5 for memory 6.4 for processor @3.1 Mhz. Not a big difference between processor scores with about a $60.00 difference in price. I bought the Sempron in a Motherboard combo from Newegg for $97.00 $141.00 total with the 2Gb of Gskill memory.
Is it possible that the Sempron has a better memory controller on it than the Phenom. I couldn't imagine that.
"Using onboard video the Phenom setup is overclocked to 750Mhz and the Sempron setup is at 500Mhz"
Overclocking Phenom video would give you a higher score.
FWIW - if both pc's do what you want, don't bother with the Windows Experience Index. Microsoft says you can run Win7 with a 1GHz cpu and 20GB HD - uh, yeah in a perfect world. My 750GB HD is 5.9 but no issues with video capture and file saving and much faster than my old XP 180GB HD.
Not really worried about the Windows Experience just a bit miffed at how the same motherboard and memory on 2 pc's with a faster CPU on 1 the slower cpu setup would give a 25% higher graphics and memory score.
The phenom setup handles HD video with ease. Don't see the benefit of a discrete graphics card when the onboard handles HD video with ease. absolutely no plans of gaming. Never was a gamer. The Phenom setup is a 100% HTPC.