I think that is one of those questions where we'll just have to wait and see. There are many variables in WC'ing a system that make each configuration unique. For example, my BSG case utilizes a 360 rad, but only has two 120 fans on it. And it cools my AM2 6000 and both 8800GTS cards with no issues.
On Trident, I will be breaking up the loops as follows: Loop 1- CPU, loop 2- GPU1 & 2, loop 3- GPU3 & NB (and possibly SB & mosfets too). I think a single 120 rad would be sufficient for each of the loops, but as I said, it will be a wait and see. I will also be toying with the fan directions to see what gives me better numbers.