With my recurves, I shoot 2-under (index and middle fingers). One is 45# and the other is 48#. I don't think I could go beyond 50#s, though.
Accuracy is much better than any other way (i.e. 3-under or split-finger). Makes sense. Less contact with the string means less potential for problems.
My 47# longbow, however, will NOT tolerate 2-under; it insists on 3-under. Don't know why but it does.
I use a tab, though I cannot find a 2-finger under tab. Is anyone aware of one?