I'm planning on building a PC in the near future and I'm constantly keeping in mind how the hardware would perform with these 2 emulators. Here are a few things I've picked up...
1. CPU performence is more important than GPU performance. The more Ghz, the better. While it helps to have a dedicated video card, it isn't nearly as important as CPU speed.
2. Intel's perform better than AMD with these emulators. Read the thread I'm about to provide at the end of this post and you will see many people with intels that get bettter performance than their AMD counterparts which have higher CPU speeds...
As for me. Both of these emulators perform rather well on my new laptop. I have an i5 clocked at 2.4Ghz and turbo boost up to 2.9Ghz.. I also have a better GPU than you (Intel HD Graphics 3000)
I get full speed on most of the gamecube game I have and 95% on Mario Kart wii. Also get full speed on Jak and Daxter with the resolution up rezz'd 2x...
So my reccomendation would be to save and build your own PC like I am planning on doing.... You could probably get some very good speeds if you bought an AMD phenom 4x black editon and overclocking it to about 3.8-4.1Ghz.... They are reasonably priced.
(unlike Intel)
To get a better idea on the whole AMD vs. Intel and weather Quad Cores are better than Dual Cores I would take a look at this thread....
http://forums.ngemu.com/showthread.php?t=126268
(^ I think the author of that thread was reading this thread a few minutes ago!)