We ran the two types of 10 x 1 arms at Gulf Coast RC Race Track
which is a long outdoor track. We found that the round wire arm is built on a heavier blank. This makes it a little more powerfull and gives tremendous acceleration from a rolling start like coming on to our straight. The flat wire accelerated a little better out of the hairpins, but was a fairly soft running motor with good corner control and predictability, less top speed and slower but more consistent lap times. It would be better on a shorter track as advertized. The test description starts here
on this web site and will continue with a couple of custom wound arms on the same blank, one round wire and one flat wire, a little later.