Unfortunately I don't have any personal experience with either of those cards, so I doubt I can tell you anything you don't already know or have read. For me it would come down to cost; yes the Gigabyte card is clocked quite a bit higher, but it's not really worth paying a massive amount more for, as you could easily overclock the Palit to the same level (if they're the same price, or pretty similar, then yes, by all means the Gigabyte is the one to go for).
As for alternatives, well, the ASUS DirectCU II, MSI Gaming, and EVGA Superclocked are all solid cards, and have had good reviews. They all perform largely in line with one another (or within easy overclocking distance); so again it comes down to the cost where you live. If I had to choose one, I'd probably go EVGA or ASUS, but that's just me.
Also, If you're thinking about water cooling, it would be worthwhile checking the ease of availability of the cooling blocks you'd need; some cards have custom designed boards, which can occasionally complicate things a little.
EDIT: Just to clarify though; I personally would probably stick with the 670 SLI you currently have if I was planning to stick at 1080p, and save up for when the high end Maxwell cards hit (probably 2015).