Well,there are plenty of articles about this on the world wide web of course.Even though it's more efficient to have water draw the heat away,for our trucks and typical boost levels,I think most,if not all of us with air to air coolers, have found this to be more than sufficient without the the higher cost of a water to air system.I have two trucks with air to air coolers and I'v never been in want or need to reduce EGT's any more.
I personally think it wisest to go with a more affordable air to air and save the additional cost or put it somewhere else in the truck if you feel the need to spend more....Like putting it towards the hydroboost brake swap.