To calculate tire sizes i like to go to this site:
http://www.miata.net/garage/tirecalc.html
The 325/60-20 has a diameter of 35.4 and the 335/55-22 has a diameter of 36.5. The toyo M/T is being run by many people and you can look up old threads using the find button on people that are running the 37's as to if they rub or not. The consensus i have drawn is most do some dont--or some say they dont. The 37x13.50-17 is 37.1 in. tall(according to
http://www.toyo.com) so the tire you are looking at is actually slightly shorter, but potentially wider. Another aspect you will want to look at is the offset of the rim. The find button on this will give you lots of information.
I like a more "squared" tire than the BFG so i went the the ProComp extreme all terrain in a 35x13.50-20. I find the BFG's balloon out to much between the rim and the top of the tread. Mickey Thompson also makes a nice square wide tire(i think its the baja radial atz). I also was thinking i wanted the biggest tire rim combo without worrying about rubbing and other complications but as i researched i decided to settle on what i knew was a safe bet(35's instead of 37's) but im really happy with the result even though i thought i was settling.
Here is what the 35x13.50-20 ProComp on Kaotik NT-1's look like:
The Kaotik rims are wide(20x10) and the tires are wider than most 35's so the affect is WIDE.
