try hitting up an i5-K + GTX670, the best combination yet in my book. you wouldn't be needing an i7 unless you do stuffs that loads all 8threads.
you should hold back until march(ish)-2013 though, haswell and GTX7## would be saying "hi!" by then.
also about a "worth" table i made up, hope it helps.
i5-3330 @ 3.6ghz(max turbo 4cores) : $190 = 0.01895 ratio
i5-3450 @ 3.7ghz(max turbo 4cores) : $195 = 0.01897 ratio
i5-3470 @ 3.8ghz(max turbo 4cores) : $200 = 0.01900 ratio
i5-3550 @ 3.9ghz(max turbo 4cores) : $210 = 0.01857 ratio
i5-3570 @ 4.0ghz(max turbo 4cores) : $215 = 0.01860 ratio
i5-3570K @ 4.1ghz(overclock breakeven) : $215 = 0.01907 ratio
note: ghz/price, higher ratio = more worth it
note2: theres a 4-bin over turbo trick to reach that max turbo
note3: newegg prices
ITX rigs are awesome, lian-li or Bitfenix produces fine ITX cases that can hold plenty of HDDs as well, i've seen one of those ITX rigs that fitted a 10" double-slot GPU with four harddrives and one optical drive. the tiny thing can run BF3 1080p-ULTRA, priceless, the guy uses it as a lan party rig.
the only down side of an ITX rig is that you cant slap in extra PCI-E cards or go dual GPUs, hit an MATX if these downside concerns you.
depends on how you'll be getting the open-box items, i've had horrible experiences with open-box via delivered on some not-so-known seller, i had to pay shipment to exchange the item =( quality control seems scarce on open-box items...