Daz is right on. the performance with the 100 was excellent, but acceleration from vertical was MUCH better with the 120. The 91 had enough power for sport aerobatics and would hang on the prop but thats about it. The extra weight of the 120 didn't seem to effect the plane, but the extra fuel consumption shortened the flights. I have not had the problem with my tank, but I have seen this before with seamed tanks from a number of manufactures. The Dubro is probably a good idea just for peace of mind. :^)