4gigs is FINE! What processor are you using? If you're using any AMD or an i5, 2x2gb is perfect for gaming. If you're using an i7, you'll want 6gb (3x2gb) since the i7 utilizes tri-channel ram to get the most performance.
In real world gaming... the difference between ddr3 1600 and 1333 is virutally nothing. Same goes for expensive memory with better lateencys, unless you're overclocking through the roof and running Crossfired 5970's, its not going to make a difference... as your games will still be limited by your graphics card.
If you're on a budget, check these out http://www.newegg.com/Product/Product.aspx?Item=N82E16820227558
If you can afford to spend a little more, i'd recocmend this: http://www.newegg.com/Product/Product.aspx?Item=N82E16820231278
No reason to spend $200 on rAM kits with 7-7-7-20 timings