Bottlenecking problem RAM/OC cpu problem *please respond fast*

Im thinking of buying a PC and here are the specs of what im buying:
Im in australia so idk if that changes anything.

CPU: Core i7 920 2.66ghz (Will overclock)
Mobo: Asus p6t Deluxe v2 (Heard form many forums its the best overclocking motherboard)
Heres where my problem lies: i WAS going to get: 12GB of 2000mhz RAM Corsair/Team Xstreme, BUT i found a forum saying to use less powerful ram to stop bottle necking in OCing.... Now im not familiar with bottle necking so could someone please explain?
I thought getting a TON of ram with high power would really increase my Computers speed and performance, but is it a problem for OCing?

Im also going to get it Liquid cooled, and have a GTX 295 Graphics card with it just so you guys know.
(Obv. Putting it together myself.)
Oh and i can only get Vista Home Premium 64-bit if you need ot know that info too.

Please respond soon, because idk what bottlenecking is and it sounds like its a problem, also im new to OCing, never done it before so use terms ill know please.

This is going to cost me all about AUS: $2500 but im ok with that
Thanks!

Oh and in anyone else opinion is it worth paying ALOT more money for those? Or should i just get 6GB/8GB of 1600/1333 ram and a GTX 275 1792mb 448bit 715mhz DDR3 graphics?
It would cut the price down ALOT, and i would be wanting to use it for hardcore gaming later on, and for it to last many many years, thats why im paying so much os i will not have ot upgrade for a very long time.

Also, i got a USB External 1TB HDD, so it would only have a 320GB Internal, But i do want to OC this as much as i can without reducing its lifetime. I do alot of 3d and 2d work too so the ram i do need alot of aswell as graphics, so any help with this would be great thanks

Sry didnt know there was an edit button, btw im looking at the ram and it has changes between CL6 AND CL7, whats that? and 1.65v and 1.8v now i heard something about OCing has somethign to do with that, so please go in depth with that too if you can.
P.s (An 750w PSu i think i added ot the cart, not sure if i need more, i htink combined with the CPU GPU and water cooling i htink ill need more, not to sure.... Oh and the 2000mhz ram is 1.9v and CL9...... please explain
They are all corsair i dont think ill go with any other brand because these are dependable and reliable.