CFM does relate to RPM's. The faster the speed of the fan, the more CFM or air pressure usually. The problem is that the faster the fan spins and the more CFM it puts out, the noiser the fan is.
I didn't look at the fan selection here, but a popular fan for this cooler is the Panaflo H1. That is the high flow or high speed version and I believe that it is in the ballpark of 30 db (decibals or loudness) and puts out close to 40 cfm. This is the fan that most OC's use.
I do plan on getting this cooler for an Athlon XP. I will probably end up using a low speed quiet fan because the XP is a cooler chip and I don't plan on OC it. I'll probably use a PC Power and Cooling Silencer or a Papst. The Papst only puts out 20 cfm at 15 db's and the Silencer puts out 28 cfm at about 20 db. Both of these fans will be inaudible. I will probably just stick with the Silencer on this because I already have one and the Papst is about $20 from plycon.com.
Because the 8045 is a massive hs, you can get away with a lower cfm fan, but it all boils down to what you are planning to use the cooler for. If you are planning to OC or if you have a hotter chip like a faster Tbird, you might want more fan. Truth be told, a 30 db Panaflo will probably be silent and give you excellent cooling. There is no reason to get one of those Delta hair dryers for this HS. That's for sure.
Sal