Multi Client vs Multi Boxing setup

I am looking at doing a 4 box or 4 client setup. Right now i can get 3 clients running (Wtih some lag) on my 2800+ system with 2gb of ram and a 6600gt(128mg) card.

I want to end up with 4 clients running (Wife says i cant do 5 clients since she would never be able to group with me again :lol: )

Looking at prices for parts, power, broadcast setups. Is the easier route going 4 dps type characters doing a single box with several clients running or doing 4 boxes total?

I am looking at upgrading the current system for around 808.95 + tax & Shipping. The question is will my 4 client setup work as well on a very beefy computer vs 4 mid level systems linked?

Second part is if the single box, 4 client route works while using keyclone, will i get better preformance on using a single high end card or going SLI? I would like to move towards two 19 inch Widescreens.

Thanks for any advice :)

XFX GeForce 8600GTS 256MB GDDR3 PCI Express x16

Patriot eXtreme Performance 2GB (2 x 1GB)
&
Patriot eXtreme Performance 1GB (2 x 512MB)

AMD Athlon 64 X2 6000+ Windsor 3.0GHz Socket AM2
EVGA 122-M2-NF59-TR Socket AM2 NVIDIA nForce 590 SLI MCP ATX AMD Motherboard

I am running atm 5 clients on my machine (2.4 intel duo core, geforce 8800GTX 768 mb, 2 gb ram (will get more soonish ;)) with 2x 20" monitors. Binding them all with autohotkey + some other hardware. For now (5x 19 lvl characters) it works fine, probably will have to change something for lvl 70 pvp.

1 main window on 1 screen and 4 others on another screen. Getting some lag in capital cities, but outdoors and in instances works just perfect.

are you running a single card or 2 ?

Also what "Other" hardware are you using with the setup? Xkeys?