CPU is almost irrelevant - CPUs are pretty maxed out.. (although, with your laptop specifically the Intel 4000 gfx relies heavily on the CPU so there would be a benefit to your lappie having at least an i5, but;
your focus in my opinion should be on getting a laptop with the best damn video card you can get.. and definitely ensure it has SSD.. RAM you definitely want 8GB(6GB is good enough I guess but 4GB is definitely showing it's age..
I guess you could do what almost no one ever does and get a better CPU for that laptop and also look at SSD
because you have an ASUS laptop at the moment I've gone to ASUS.com and ticked "Gaming" in the laptop category, check out the specs on these actual gaming laptops.. http://www.asus.com/nz/Notebooks_Ultrabooks/Gaming_Products/
DDR5 video cards
SSD
higher resolution., etc
don't buy a mini if you're planning on racing against ferarri's !