Always go with a 1600mhz, as long as your MB supports it, most do now a days, buts its always nice to check before ordering. 1333mhz RAM runs at a lower speed
I'd recommend this RAM though
Crucial Ballistix Sport 8GB http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Spend the extra $8 and double the memory you were going for
Your motherboard supports up to 16gigs of ram
I have the same RAM. I just checked your motherboard's memory support list and PNY is not listed. The PNY RAM will most likely run at 1333MHz. I believe the Crucials are supported, so I would go with them. Check your motherboard's memory support list just in case though.
Overall make your system run better. If your playing a game, 8gigs will be able to be able to split up better between the game and OS, say 50/50 for example. 4gigs to OS, 4 gigs to game. With 4 gigs, 50/50 would be 2gigs each. that's just an example. Don't expect it to split evenly.