If you're comparing between both 780 Tis (Gaming vs. Classified) I would say get the cheaper 780 Ti and use the $100 towards watercooling. The only difference between the two is going to be whatever pre-overclocked settings that the manufacturer has gotten to on their own, which means you can easily try OCing yourself a bit to make up the difference.
Not to mention several reviews have praised the 780Ti for it's surprising amount of overclock headroom. If not the Gaming one because of fan oil issues, maybe look for a different cooler at similar pricing and apply the same logic (overclock yourself over paying for the manufacturer to do it)