This thread has comments about "the" Maxxair and "the" Fantastic. I just spent three hours wading through the specs for dozens of models for both. There are some pretty drastic differences. Here is a table for the Maxxair models: http://www.old.maxxair.com/oem/search2.php and Fantastic: Fan-Tastic Vent's Retail 12 Volt Fans
Also bear in mind that both of these companies have old models and new models, many of which are similar in some respects, but have totally different model naiming systems.
(BTW, I settled on the Maxxair 6201K.)
Hi: sharpstick... Good choice!!! Here's pic's of the MaxxFan I put in our former Boler.
Alf S. North shore of Lake Erie
Most of the modern ones are rated 900 or 920 CFMs. I just installed my Maxxair fan and it's pretty good, but 920 CFM is the entire volume of the Burro and then some. It has nice flow, but it's hard to believe that much.