Although opinions seem to vary... The Ramtec in my opinion is the faster of the two in the air but the Dynamax is better at getting you up-there.
Much depends on airframe and engine combo, not to mention setting up with a good pipe... So with this in mind, this is why we have the two schools of thought as to which may perform better than the other.
If you really want to open up a can of worms try asking how much thrust each can produce : )
Not much difference at the end of the day really... Both are very well made fans IMHO and very good products. Give Ed and Kevin at Great Northern Models a call if you want further info on the Ramtec as they are the North American distributors for Trim/Ramtec

Cheers-