There is a lot of talk about this over at the RC Tech 1/8 conversion thread:
http://www.rctech.net/forum/showthre...58327&page=148
It sounds reasonable to me that the 1509 would be more drivable in a buggy and the 1512 for a truggy. Problem is, none of this has been tested. We raced last summer with MM/1512/4s combos in our buggies with great success. 20-25 minute mains without thermal (about 165 degrees F on average). I think a 1509 in a buggy would run hot, but I have no scientific proof. I also think a 1512 would be too small for a truggy. Just my opinion, again.
I run a 1515 1.5d/f in my truggy and have no problem at all with the power. The tires stay firmly planted to the track. I have no punch control other than my trigger finger. I think a lot of guys need to use the throttle finger more effectively.