Need some help here guys.
I'll try my best not to confuse you,so here goes.

I have an AM2+ mainboard(M4N82deluxe,supports AM3cpu) with a Phenom II X4 955 CPU clocked to 3.4 with 4 gig of DDR2 @ 800Mhz.This is using all 4 DIMM slots.
The mobo manual states it can run up to 1200Mhz ram O.C,but supports 1066Mhz standard,but only in 2 DIMMs.If i use 4 DIMM slots it drops to 800Mhz for stability.Now atm,i have 4 DIMM slots used with 4 x 1gig modules @800Mhz,but in the BIOS i have the option to OC these to 1066Mhz.
Im using Vista 64 so i was thinking of upgrading to 8gig.

The question is,does anyone know if i will be able to run 4 x 2gig DDR2 1066 modules using 4 DIMM slots at 1066Mhz?
Or would i be better off going for 2 x 2gig DDR2 1066 modules and try to OC these towards 1200Mhz.
Will there be a substatial gain in performance from 4 gig 1066 to 8 gig 1066?

AM3 is not an option here as GFX are running in SLI.Im trying to keep cost down but want more speed. Greedy i know,but i have the need for speed.

Mosts Boards have trouble if you equip them to all Slots, the best way is to use just two slots with higher GB Rams, I used 4 slots each 1 GB before and system was not starting, so I had to put the Ram-Voltage up. I could´nt OC my CPU without RAM-failure and auto-reset at the normal settings. But now I am using 2 modules each 2 GB from Corsair ( Dominator :-)))))) ). No problems at OC ( even I don´t OC any more cause my system is running fast enough at 3,0 GHZ ) I am using 1066 MHZ Corsairs and they were testet by OXC for 1200 and they did it. But there is not a big difference between 1066 and 1200, thats the reason why I don´t OC and risk my warantee and the longtime use of them. Maybe you get more use of it if you can try different latenzy´s like 7-7-7-15 ore what ever their spec is. But the most important thing is that you take a look at Mainboards QVL-List, there you can see what RAM is ok for this Board. Maybe check some shop sites and look if there is anybody who bought them and running right on this Board.

Hope I could help you a little out mate!

Don´t forget the divisor of the clockrate in your Bios, maybe your ram is already running with higher settings cause you havent chosen the right divisor while OC the CPU.

Yep I'll agree with that.

Mobo's don't tend to like all memory slots used, don't know why. I would go for the 2x2GB option Paul and overclock (it's not like you'll be any quicker with the frags ).

What make of RAM do you have? I had issues with OCZ in my machine, the RAM was ok in a friends machine but my Asus mobo wouldn't have it. Swapped to Crucial ballistix and never looked back, overclock real well. So you could flog your exisitng RAM and try another manufacturer???

Doubt very much you'll notice any improvement from 4GB to 8GB to be honest, especially gaming.

Thnx fella's,
It looks like i might have problems and waste money if i go for 8gig.
This machine is not for gaming but for GFX apps.
In my gaming rig i do have 8gig Dominator 1066 and it is fast.

The heatsink i have in the new machine clashes in height with the first DIMM,so can't test the Dominator in there.

The RAM i am using atm is Corsair XMS2 6400 @800Mhz.
The new RAM i am looking at is:
Kingston HyperX 4GB (2x2GB) DDR2 8500C5 1066MHz

Stock,oddly enough, runs at 800mhz 5 5 5 18 1.8v,but if i up the voltage to 2.2v it auto sets to 1066mhz 5 5 5 15
Its listed in the QVL,so thats cool,im just really tempted to go 8gig but do not want to waste £80.
Im going hold fire for a little while longer and see if any more replys come in with some more advice.
Thnx for your help Baks and Blue

i dont think you will get any better advice than whats been offered upto now.unless you upgrade your mobo and get a ddr3 board and a high end one at that.

Haven't bought any yet but thought i would try and get the timings tighter on existing RAM.Failed to boot a couple of times but now think i have hit the mark.
Got these running now at 4 4 4 12 @ 2.1v and flying.Seems very stable atm,been stressing them and all is fine.
They were running at 5 5 5 18 @ 1.8v but now loading times are very quick.Im very happy and a cheap upgrade

so hows all this done then...is it a bios thingy tinkering job or what?

please reply in baby talk so us 60 yr old under stand!!

Yes it is altered in BIOS m8.A dangerous place to be messing about if you are worried about creating a nightmare.I'm relying on someone to shout out to let me know if im going wrong somewhere

I have run memtest86+,orthos and prime95 to test and stress and all seems to be stable with no errors.

If you want to know which is the best and most compatible memory to use check out the "qualified vendor list"
uk.asus.com/Search.asp...2%20deluxe

Its Asus own list of memory that has been tested to the max, and proven to work fine with that board! Select which board you have then memory support list and down load the list. Will contain all known brands that are compatible 100% with your board!

Thnx Cap,
Very helpful m8.The QVL d/l from Asus has more products than the list in the manual for the mainboard that i have.
2GB DDR2 @ 1200mhz x 2 sounds just what i need.