Looking to replace my Alienware M5750 (5 years old), with a refurbished or used AW M18X. Any experiences buying on used or refurbished?

I've identified about a half dozen I seriously am interested in. The main question is do I go for high end processor or high end graphics see my list and give me your choices. I used to be a big first person gamer (Doom, Quake, Unreal, Duke Nukem, Rise of the Triad, and Castle Wolfenstein) and I will probably pick up one or two of the newer titles. I will probable keep this system for 5 years as well. I do a lot of excel spreadsheet stuff and all the basic stuff. This is a desktop replacement, I sometimes bring to work for fun or having a second screen on a big project.

Intel Color RAM VIDEO SYSTEM HD
3820QM RED 16GB GTX660M (2) 256 SSD
3630QM BLACK 16GB GTX660M 128 SSD / 500GB
2670QM BLACK 8GB GTX580M SLI 750GB
3610QM BLACK 8GB GTX660M 750GB
3920QM BLACK 16GB 7970M CROSSFIRE 500GB
3720QM BLACK 16GB GTX675M SLI 256 SSD
3820QM BLACK 16GB GTX675M 500 GB

Processor Speed Pass Mark Benchmark
3920QM 2.9GHz 9149
3840QM 2.8GHZ 9023
3820QM 2.7GHZ 8811
3740QM 2.7GHZ 8573
3720QM 2.6GHZ 8404
3630QM 2.4GHZ 7768
3610QE 2.3GHZ 7690
3610QM 2.3GHZ 7539
2860QM 2.5GHZ 7240
2670QM 2.2GHZ 6099
2630QM 2.0GHZ 5631