That cooler will lower temps a bit and prevent any throttling, but the real issues are the lack of custom PCB based Titan's and the lack of voltage control. 780s are much more versatile in this respect (two models will have voltage control), and scale much better from the base GTX 780 reference configuration as a result. Also, the 6GB of GDDR5 on the Titan further takes away from the TDP headroom for overclocking.
I think Titan has uses for surround (as it has a ton of VRAM), but for single screen gaming or even triple 1080/1200p.......I think i'd take a custom PCB GTX 780 over the Titan anyday. As I said this cooler solves only half the problem. It doesn't give the Titan voltage adjustment or more available TDP headroom for overclocking.
It makes me wonder why nvidia is allowing AIB partners to go nuts with custom 780s, yet the 1000$ Titan is completely locked down (no custom PCB, no non-reference cooler unless user installed)? Doesn't make sense to me, if anything it seems like the other way around would make more sense. Whatever though!