Originally Posted by Imglidinhere
You won't have to overclock it because it handles that with Turbo Boost. It pushes up to 3.33GHz on it's own for a single core and naturally pushes up to 3.06GHz for two cores.
As for selling the machine, the performance difference between a Sandy i3 and the i5-580M are nil. Essentially it'd be a sidegrade in every respect, with the benefit going to the i5 moreso than the newer i3.
OP said he wants to play BF3. GMA HD graphics (what all 1st-gen Core i CPUs have) doesn't have a chance. HD 3000 *might* do it on low. HD 4000 would be a decent option, again on low.
Otherwise, your analysis is correct IF you're assuming OP will do the external GPU thing.
3rd gen, Ivy Bridge graphics: http://www.notebookcheck.net/Intel-HD-Graphics-4000.69168.0.html
2nd gen, Sandy Bridge: http://www.notebookcheck.net/Intel-HD-Graphics-3000.37948.0.html
1st gen, Arrandale (what you have): http://www.notebookcheck.net/Intel-Graphics-Media-Accelerator-HD.23065.0.html
Huge performance difference between the 3. 1st gen can't play D3 on low, 3rd gen can get >60 FPS on low. D3 is a very lightweight game (similar to GW3 in terms of hardware needed). Now, HD 4000 can barely play BF3 on low (25 FPS or so..), there's no way HD 3000 or GMA HD will. HD 3000 and higher can play Guild Wars 2; again, I strongly doubt GMA HD could.
Best option would be trying to score a used A6 system with 6630M (or higher) graphics. A6-34x0M series is about tied with HD 3000, A8 (either series, 45xx or 35x0) is a little faster than HD 4000, and A10 is on average 20% ahead of HD 4000 (though, it beats HD 4k by 50% in some games.. while it typically loses by <10%).