I'm no expert by any means, but it seems to me that the second system is worth paying the extra money for? Surely they'd both run all 3 games that you've stated at close to Full detail.
Slow reply I know, I've only just found this section of the forums again :P
Like I said I'm far from an expert but for your basic use requirements and games you've mentioned both systems should be fine.
Maybe I'm wrong:P