I have a G502 Proteus and it has put my fps gaming in a new league. Just remember that a good mouse mat is just as important as a good mouse. I am particularly picky when it comes to mice and can tell you to stay clear of those ambedextrous mice at all costs. If you think about it, there is no particular reason to have one and they feel terrible. Before the G502, I tried many other mice, including the oroborous from Razer, which costs a whopping $125 and nothing fits my hand like the G502. Also keep in mind that you have 3 types of mice grips: Palm, claw and finger. Which one are you? Then lastly, the weight of the mouse does make a difference, as a heavy mouse leads to fatigue if you play long sessions.
On keyboards, I've heard good...