A 360,2 240s and a 120 is definitely overkill And heavy on the pocket! There comes a point where you add extra rad area and it doesn't affect the temps much,
the point of diminishing returns!
When running Furmark and Prime 95 32k in place FFT's I can safely say the 2 240s are getting warm but the 120 (last rad in the loop) isn't getting anywhere near as warm
so the lions share of the heat is dissipated by the first two radiators.
I'd say a 360 and a 240 should be ample to be honest, and use the money saved from not grabbing the extra 240 and 120 on some really good fans and add a bit to the new GPU fund..
I think i'm at a similar point to you at the moment in terms of upgrades too, instead of going SLI it may be more prudent to keep the money you've saved for the second 680,
and sell your first 680 in order to grab a decent single card setup, this will reap benefits in more vram and less headaches!
Not all games support or scale well with SLI and ofcourse you will drop some frames as the mobo will go to x8/x8 or 16/x4
which will not work with SLI as apparently you need a minimum of x8 lanes.
IF you had a 3rd gen i5/i7 the difference in the GPU's running half bandwidth would be less as the Ivybridge cpu's are generation 3 pci-express so have more bandwidth available than the chips we're using
Spank the 2500k up to 5ghz and reap the benefits!