If you use the 9411, you will be giving up 34 oz. in. of torque. The 2721 will be the better choice, especially at high speed. Both are ball bearing, coreless and metal geared.
I have both types of fins for mine, (swept and standard) and have installed 8411's in them.
I was one of the two guys that had a rudder failure on a Balsa Bandit when they first came out, and am lucky to have been able to save the plane. The gear train was too weak in a smaller (easier to install servo, which is where I think you might be heading) as was the servo output arm......going with the stronger servo will be safer in my opinion....
Don't forget to install the leading edge fin bolt..............that is why I was able to save mine.....it kept the fin from departing.


Harley Condra
BVM REP
JetCat REP