The dell has an i7 quad core with hyper threading, the asus has a dual core i5 with hyperthreading. Basically, the i7 will act like it has 8 cores, the i5 will act like it has 4. They are roughly the same processing power per core,(the i7 is a little better due to higher clock speeds) so the i7 will be faster in multithreaded things, like compressing files, and stuff. For gaming, however, both will be plenty fast enough and shift the bottleneck onto the gpu, making the asus better at gaming.
Also, the asus cpu is rated at 17w, the dell at 35w, sothe asus will use less power, leading to (probably) better battery life.
I spent roughly 4 months looking around before i bought a laptop for school/gaming. Now I regret buying a gaming laptop, instead of building a $600 gaming pc myself, and getting a cheap notebook/chromebook.