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I'm running a 4670 non k as I dont do overclocking but might be getting another 290 for crossfire. Is it worth me selling my 4670 and getting a i7 with HT such as the 4770 or haswell refresh?
It's probably worth getting the 2nd 290 first. See if the CPU is holding the GPUs back before upgrading. Can your motherboard overclock?
from sandy to haswell 5-10 percent difference.
http://wccftech.com/intel-sandy-bridge-ivy-bridge-haswell-graphics-compared-10-difference-average/
only difference as mentioned in games i5vsi7 is if you go more than one card you'll notice it otherwise no difference.
hyperthreading has it in its name HYPE literally no game makes any benefit of it and even bf people ive asked showed no difference.
so single gpu take your pic 2 cards go i7