I use a 3w pot on a Sunon 120mm fan. I think it's rated for 83cfm. I turn it up/down depending on my needs. I usually just monitor the air temp of my heater core. I can't tell you rpm though 'cause it,s only a two wire fan.
I use a heater core from Nissan (if a remember right). It is large enough for holding 2 119mm Papst 4312L fans (55.9 cfm, 30 dBA) in front. In normal use I have them turned down with a pot (rheobus) to about 2/3 to keep returning water at about 23-24°C (ambient 20-21°C). For performance (o/c) I bypass the pot.