No budget range.
Primary use is for gaming.
Only parts required are those below.
Novatech.co.uk or ebuyer.co.uk are preferred retailers.
Possibly overclocking in the future (yet to learn).
1920x1080 is my monitor resolution.
Straight to it. This will be my first build and I just need to know if it's all compatible.
B* These are the only parts of the build I haven't aquired. If this is compatible is a 650W PSU capable of handling it?
C* Is there any significant increase in performance between 1333 & 1600 RAM clock speeds on an i5 2500K processor?
D* In terms of longitivity, what can I expect from this build? (i.e. how many years am I looking at before a next upgrade is necessary)
D2* What is most likely to be the first thing that needs an upgrade?
B. Yes. 1 HD 6970 only.
C. No. Any slight difference in dwarfed by even a minor overclock of the CPU.
D. As long as you're happy with the performance. If you play 2010/2011 games over the next decade you'll be fine for 10 years. Otherwise the most common upgrade is a mid-life GPU upgrade to handle then current games. You'll have the option for a CPU upgrade with the next gen Ivy Bridge CPUs but likely won't need it.
I guess it most depends on how your budget is doing. If you're not going to be limited in some other area (like maybe not getting a CPU cooler?) to get the RAM upgrade there is NO downside to getting the faster RAM. If everything else is taken care of and you're not cutting corners elsewhere it's a fair use of an extra fiver or so.