John,

The 3301's required for the elevator are probably the area that is least flexible in terms of alternative servos. The stab is just so thin at that point (it's a diamond airfoil, BTW) that the other servos you listed will not fit.

For the rudders, there is enough room for a bigger servo. Only problem might be weight. BVM states that nose weight will need to be added if you use e.g. 4131's in place of the 3421's for the rudders. The 3421's are 1.04 oz; a 4131 is 1.5 oz; your 2721's (as an example) are even heavier, at 1.84oz. (I didn't check the weight of all of the servos you quoted; some may be less).

This added weight is quite far behind the CG, so you need to be careful about how much of it you take on.

Sorry - I know that's not really the news that you wanted to hear !

Gordon