I have wondered how to do the same thing myself, many times.
The best n-1 of n is easy: just use sum()-min() where the parentheses
contain the range (you have to fill in zero's if there are any
missed assignments).
For best m of n (m<n-1) I copy the n values to an empty part of the
spread sheet, sort them, and sum the first m values. I suspect I could
write a macro to do this, if only I knew how to write macros!
But maybe there's a better way...