Watercooling is definitely not necessary either way. And it depends what you will be doing with it. The 780 Ti will last and perform longer for future games. If you're planning on something like Star Citizen, then you'll definitely notice a difference.
if you want good fps on ult at 1920x1080 and save money. i think GTX 780 should be fine.
but if u want more resolution, i think at ult better GTX780i, because the different between GTX780 and GTX780i at 1920x1080 not so much..
At your resolution, with a MSI GTX 780 Ti Gaming, you are looking at a 21% performance advantage over a GTX 780. That may be a big enough advantage to be worth it if you have the money. Check the rest of the review to see how that translates into specific games.
Picked up my GTX 780 Ti today. I gotta say, the reference cooler is very cool. It's much beefier and heftier in person than you would think and it's pure solid metal throughout. It reminds me of a classic 60's muscle car with chrome fenders and mag exhaust pipes getting ready to race the quarter mile.