I put some .14 speed digitals in a profile plane where most folks just use standard servos. They are quick and precise, but probably not necessary.

I let a 3D master fly it..this guy is amazing, one of the best I've seen (who BTW runs Std servos in his plane AFAIK) and the very first words out of his mouth:

"Wow..you've got some good servos!"

So if you are experienced enough to tell the difference, I guess you can tell but I run .21 speed servos on a different profile (on 6v however) and they seem just fine to me.

As for the exponential...I use it so I can run radical throws and still fly "normal"..and I use dual rates also, but my low rates are still pretty touchy without EXP. Just my $.02