Is it right that I'm getting FPS Lag?

So I'm multiboxing four copies of D3 and I have all my settings set to low yet I'm still getting consistent lag and some screen tearing at points. The reason I'm surprised that I'm getting lag is that I thought I had a high end system that would be able to handle running four copies of D3 at once, apparently I was wrong, or maybe I have it set up wrong?
System Specs:
CPU: AMD Phenom II X6 1100T Black Edition 3.2 Mhz
6 GB of Ram
GPU: Evga Gtx 670
My hard drive is 500gb normal hard drive not a solid state so I understand that it's normal for me to get lag when I first log into the game as it's "loading" and whatever but this lag persists and it's getting kind of annoying.
Anyone who can help will be appreciated, thanks.

[lax]

HOWTO: Tweak your framerate has tips, and information on how to identify your bottleneck

I'd say 6 gigs is cutting it fine for 4 clients...I recall each client taking about 1 gig...which leaves 2 gigs for OS and background services.

Also Diablo has a habit of choking (freezing for several seconds), this happens on single clients too :<

Agree with Marshboxer that 6 gigs RAM is cutting it close.
I have 4 gigs currently, 8 gigs by end of day today.

With 4 gigs I have EXTREME lag on 3 clients for loading etc, and am completely unable to run a 4th until my RAM arrives today.
I would feel like I would probably be in the same situation running 6 gigs with 4 boxes as im currently in with 4 gigs running 3 boxes.

I dont think I would advise less than 8 to anyone wanting to quadbox diablo even on min settings.

Ah I see so I need some more RAM then yeah it turned out that my botleneck was ram so there's the problem anyways thanks for the tips I thin kin my channels currently I have 2x2 gb and 2x1 gb so I need to replace my 2x1gb with 2x2 gbs