Nvidia card choices (680 vs 660ti SLI and 670 SLI)

So, long story short I have a brand new Gigabyte 680 OC 4gb that was faulty from arrival two weeks ago. I bought it to upgrade my old rig, and through the faullt dianosis process (long ass story) I ended up buying a new pc... and building it from scratch. Now I have a Z77 with i5 new ram and dual SSD's.

With the prospect of the RMA card being refunded I have started looking at other options.

I want 3-4gb for "future proofing" and cos I play alot of modded total war games that use alot of vram. Also only want Nvidia. Dont care for ATI. Added to this, based on the cash I have spent i want to be able to play games on max settings, kind of pointless spending all this cash otherwise. Especially important is to be able to play Rome II total war in full detail all Ultra settings...

After some research I am stuck between these choices:

- Buy another 680 4Gb OC

Pros - single card so minimal micro stutter, cheapest option
Cons - performance already challenged by some top end games, may be "outdated" soon and require additional card to be bought anyway.

- Buy two 3gb 660Ti's in SLI

Pros - Better performance than single 680.
Cons - £80.00 more than single 680, micro stutter, only 192bit interface, less vram.

Is the 192bit interface a real issue. I read that it could impact top end performance. particulalry with reagrd to AA settings?

- Buy two 670 4Gb OC in SLI

Pros - Better thn either of the above. (256bit interface up from 660ti)
Cons - £250.00 more than 680, or £180.00 ore than two 660Ti, micro stutter.

Are two 670's worth the extra? after having just spent £1600.00 on the new setup (including 680) an extra £250.00 could be justified if it makes the real differnce between a killer setup that will last, and a limited one that will quickly need another upgrade ayway.