Well, you could always try for an AMD Radeon HD 7970, but I don't think it'll be able to maintain at least 120fps.
Your best bet will have to be the GTX 780. That, or something like two gtx 770's or a gtx 690 (kind of no point in getting a titan as the 690 outperforms it in almost every way for the same price, unless you need the extra vram).
If the AMD Radeon HD 7970 does not give you at least 120fps stable, there is no reason to get any amd card. Two 7970's will be too noisy and produce too much heat and the 7990 gets outclassed about half the time by the 690 and also producing tons of coil whine and heat.