I would go with the T5750 Processor and a ATI Mobility Radeon HD 3650 GPU 256 MB.
But in this video.
This guy is playing Oblivion on a laptop with a 7inch screen. Hes basically saying you can play the game well on a slower computer.
How much memory does the 3100 have?
The difference between to processors are very little if you think about it that way. I can almost guarantee you won't notice the difference in processing power...
C-135R Crew Chief
i7 2770 @ 3.4ghz, Geforce GTX 560 ti, 8GB DDR3 1600, SSD 120gb, cup holder
I would imagine if you could understand Morse Code, a tap dancer would drive you crazy