dukzcry, the speed that you can achieve with all four dimms populated depends on a couple things.

probably the most important has to do with what processor your are using (i see that you are talking about quads) as in the specific model, and what its highest multi is--or at least the highest you plan on using.

with the quads, the MCH has to handle much more I/O than with dual core processors, and because of this added overhead it simply cannot keep up beyond a certain point.

also you have to consider that there are slight differences in the quality of MCH from board to board. for example, the x48 is simply a higher binned version of the x38. essentially all this means is that is is the exact same as the x38, but it just so happens that it is capable of "better performance" than the average x38, according to sources interviewing Intel folk.

as for how fast you can run 4 dimms with quads, my answer is going to have to be that it varies. For example, i used to have a Q6700 (1066 fsb) with 4x1gb super fast capable ram, but i could never get it 100% stable above 1580 or so with the 10x multi. now that was before i learned how to adjust GTL refs and voltages appropriately so maybe i could have got it stable at 1600 or 1610....but there is only so much tweaking you can do for stability when the processor is running flat out and everything is close to its max.

now i have a q9550 (1333 fsb 8.5x multi) and with those original 4x1 dimms i ran into similar issues at like 1602 MHz for the RAM, which was frustrating because going from 333 core clock to 400 is hardly an overclock, in my opinion. so i ditched the 4dimms and went for 2x2gb and it made a huge difference.

with 2x2g and an understanding of GTL Refs and how vFSB, and vCore, affect stability, especially with MCH and high memory speeds, i was able to reach and run a few tests (not fully stable, but pretty good) at 1840 MHz with a max stable @ 8.5 multi somewhere around 1760-1780.

now the other issue at hand is this:
i know that you are thinking about 8gb of RAM, but why? unless you are transcoding a movie with something like Premiere Pro, while at the same time working on some super complex 3d CAD thing all while having 20 tabs of IE8 open with Java on them and playing Crysis, you DO NOT need that much RAM.

Its like having Z-rated pirelli tires on your Yugo...sure they can handle speeds over 180 Mph wihtout flying apart and are so sticky that the car will hold on a 60 degree angle, BUT ITS A YUGO! Bicycle tires would provide more performance than the car could handle...

a good exercise is to open the things that you commonly do at one time or even the most that you could feasibly do at once and simply look at the windows task manager. If you have less than 10-12% free memory, then yes, more ram would be helpful, otherwise adding RAM is a waste of money. Its like having a Yacht on a 10 Acre lake....or a 7 bedroom house and youre single with no kids, no pets, no friends who stay over, and you sleep on the couch.

If youre looking for a faster system, and you already have a quad, and you are already overclocking, and you have a good graphics card (if youre a gamer) the next best place to put your money is in hard drives. they are the true bottleneck in today's computers. throw some money at some good overall performing SSDs or buy 6 raptors...2 in raid 0 for your OS and 4 in raid 0 for your games or movies or such.

sean