This seems to look like The Battle Of The Insert [big grin]
Even before you consider the shape, there is two phylosophy about inserts. For efficiency purpose, those two are far the most important.
1) Dead center insert
2) Offset insert
Obviously the dead center is the least efficient. With offset inserts, you give your self more flexibilities. Square versus circle. The square gives you four faces, where the circle give you virtually unlimited faces. This for both depend of the bit size, if you use a 1/8 bit you'll have a many of itteratoins. If you use a 2"1/2, very few itteration.
Just a thought!