The more fan the better. All rads perform within about 15% of each other so don't expect eye popping gains no matter which brand or how thick they are.
Despite the density FPI count expectations, I did find the EX to be slightly tuned for slower speed fans compared to the RS which is attributed to the split fin vs folded fin construction differences. The RX was slightly better than both using double thickness folded fin and even lower density construction.
This was an earlier version though which has since been updated but it gives you some relative info anyhow.
I would NOT recommend changing rads, you would gain more by going push plus pull (~30% gain) which is more than any rad swap could give you. Use what you have and work on optimizing fans and cold ambient intake.
Avoid sandwiching at all costs, you would have to run 4000rpm + fans in push/push/pull before you would start to overcome the air's specific heat capacity bottleneck. Conventional rads in a single push or pull condition are typically netting 70-85% air efficiency levels, so not much cooling left in the air for more exchange and the restriction losses cause more harm than good. Gotta have fresh cold ambient entering each rad or forget it.Edited by Martinm210 - 12/1/13 at 2:59pm