If High-end Gaming is your priority, then don't fill it with 4 sticks. Games usually don't use more than 3GB (as almost all are 32-bit), therefore it would be nonsense.
Also, having 4 sticks causes much more problems of instability (when bought separate, even worse), and tend to get worse timings and/or clock speed.
Then again, 8 GB should be your top if you want TOP PERFORMANCE.
G-Skill is nowadays gamers first choice (usually). Anyhow, if you buy top of the top G-Skill RAM or top of the top Corsair's, difference in fps will be no bigger than 2% (and most probably, close to 0%). Don't go nuts about it, G-Skill are usually very reliable, go for them as almost everyone does .
Corsair without a doubt. It is usually a bit more pricey but, if you have problems, Corsair support is amazing PLUS, they have a very active forum with workers that actually help the customer. The only other memory I've used well in performance machines was Kingston but, Corsair has proven slightly better than Kingstons HyperX in my machines. G-skill isn't bad but I wouldn't buy it; because I've been very satisfied with Corsair though, not that I have had terrible luck with their products. I have not had great experience with g0skill though.
And look at Corsair Vengeance at the moment. It is really cheap and performs consistently. Dominator is good and my preference but is a bit more spendy . I'm running 8 gigs of Vengeance in my most recent build though so, I would go with Vengeance at this time.