Our local dirt track has started a 13.5 4wd class, everyone participating is having a blast. One of the big problems with mod four wheel is the level of attrition. At the club level, I've seen a class of 10 get whittled down to two cars by the buzzer on several occasions. Lots of guys with the "Gotta go fast" mentality jump on the 4 wheel mod bandwagon, and end up pile-driving the cars in to the wall or other cars before the race is half over. 13.5 lap times are remarkably close to the average mod lap time due to the fact (as likely previously mentioned) that more drivers are able to control the car. Wheelers are seeing far more use at our track because of the class - and breakage is at an all-time low. All of the cars are pretty great at this point, but a free running shaft car will likely have a slight power advantage. To the guy that said the 44.3 sucks - we'll have to agree to disagree. Great car, free running, handles amazing... The issue of front arm durability is an easy one to fix with the RPM replacements.
4wd is kind of a funny class - I've seen a few guys show up with original Losi XX4's modified slightly to run a shorty come out and win against modern cars. Older Lazer ZX-5's and 44's don't seem to be at a disadvantage on the local level, either. Parts support would be my main concern - not an issue with the Associated cars.