1 - Yes. The Core i7 uses 1.6GHz when it's using all the cores, but when only using 1 or 2, it can overclock to 2.8GHz with turboboost. It's faster than the 4-way i5 procesor.
2- Of course!... in my list you are talking about number two and one respectively.
3- You would only see the benefit in energy saving terms. No performance gain.
4- Then if you want to play it in the highest settings neither one will be enough. Both can play modern games at low-mid settings.
(Personally I would go with the Asus one. Great company, great laptops, decent graphics card and great processor. Overall, pretty good laptops at a better price point.)