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Really, really no need
Plus if you were going to buy anything why even think of buying now with the next gen so near?
tbh ive not even looked into next gen stuff or when its being released
i did read about pic-e 3.0 or something like that, also it could mean a socket change new cpu then thats a new can of worms opened
with my current spec getting new upgrades or components could cost 3k
where are you getting the £3k figure from? unless you go with very top end sandy-e CPU(not due out till sometime next yr), £300 motherboard, 7970/nvidia equivalent) it wouldn't cost you anywhere near that. if your psu(what is it btw) can handle 480 sli you should be fine for newer cards as well.
Remember the Zalman cooler on those 480's is EPIC.
You can likely overclock them to ~ stock 580 speeds.
Just ensure the case cooling and PSU are upto the job.
I have a similar single card setup and the o/c headroom was huge (see sig).
2 high end gpu's - £400.00-£450.00 each
1 mid -top end cpu £400
1 high end mobo £300
1 Cooler £50.00
12gb Ram £250.00
ssd x 2 £400.00
while most of my current equipment is good its 12 months ish old
so may be £2000.00 then as i can use a few items on my PC