How come I still lagg with 6850+new comp?

Okay well, on my old computer, which had the following specs:

Intel Pentium Dual Core CPU E2200 @ 2.2ghz
4 GB DDR2 RAM
Dell optiplex 360 motherboard
NVIDIA GeForce 9400GT

I would play games like Dragon Nest, GunZ, APB : Reloaded, etc.
They all lagged except GunZ didn't really lagg much.

I thought buying (or building) myself a new computer would fix the lagg in all of them, and for the most part it did, but I still get hiccups and even lagg turning the mouse sometimes (the mouse turn lagg is more noticable in Dragon Nest)

My NEW computer that I built has the following specs:

AMD Phenom II x4 970 BE 3.5ghz
8GB DDR3 1333mhz RAM
Sapphire Radeon HD 6850
ASRock 970 extreme3 motherboard
Antec Neo Eco 520c 520w powersupply : (http://www.newegg.com/Product/Product.aspx?Item=N82E168...) <----- People told me that should be more than enough)

My friend who has a worse processor, and a worse graphics card (a GTS 250) tells me he runs those games no problems, no hiccups, no lagg at ALL. How come with my better computer, I'm getting worse gaming results? Yes I have the latest drivers, and yes I play on High settings, but Dragon Nest and APB: Reloaded should not lag at ALL with these specs..

I tried 3dMark 11 or whatever and it said my computer is the same as other similar computers but how could someone with a worse graphics card and worse processor have better gaming results than me?

And to add on to it, my friend who recently bought a GTS 250 and has a 2.5ghz Dual core processor E5200 only has 10 fps less than me in A.V.A everything maxed settings. (I get around 45 in that sniper map, he gets around 30)

Something is obviously wrong here, but what?!?!

$5 to anyone who finds me the answer.

This is really saddening me I was hoping to have a computer that could run almost every game with no lagg..and after I built it, it's not giving me what I want.