i7 also has a larger cache, again something not usually needed for gaming.
If you want the extra logical cores and cache, you can get a desktop Xeon that will give you i7 performance for an i5 price. It can't be overclocked though.
Core i5 4670K can take three GTX Titans without bottleneck. 😛
And yeah, GTX Titan is not a video card to be used solo. It is made for SLI.
If you want double or near double performance of GTX Titan for same price, get GTX 690 instead. The card has two GTX 680 (GTX 770's 95%) combined into one and can also be used in Dual SLI which would get you quad GTX 680 experience.
All in all, you have three choices -
1) GTX 770 Dual SLI $800 (The best I would suggest).
2) GTX 770 Triple SLI $1200 (Use the rest of money on two additional monitors for triple monitor playing). 😛
3) GTX 690 $1000.