Go for the standard 780 and OC it. Once overclocked, the difference between 780 and 780 Ti OC narrows to about 15%. There are often deals for $450 on MSI Gaming or similar 780.
780Ti this late in the 28nm generation is a very overpriced card. In fact, you can now get almost 2 solid R9 290s (Sapphire Tri-X) for the price of most 780Ti. Comparing OC R9 290s vs. 780Ti OC is a not contest at all.
Also, there are rumors that 880 will beat 780Ti and cost less which could send the resale value of 780Ti down by $200 in just 6 months.