Depends on what kind of setup. Something like the H50 or H70 would give you slight benefits over what you've got in overall temps and lower spikes with sudden loads. An older 1/4" system would be a downgrade. Some of the water cooling kits that run 3/8" would also be a downgrade. If you went to a nice half inch system you'd get lower temps on your CPU, much lower temp spikes, and you'd be able to run a GPU or two in the mix if you had a decent sized radiator.
You wouldn't see a huge difference either way, but you could potentially get a bit more OC and get more components on the loop (less heat in the case, less case ventilation needed). With a reasonable loop you would also see consistently lower temps.