Can any one say if there is any advantage of shifting the mounting the motors 180 Degs from where they are at the moment, I appreciate a change of prop is required but I have seen a few Quads / Hex's with this config and they explain that it's "Slightly smoother in control", could this statement be true?
I assume you mean upside down?
Mounted above the boom means that the prop wash hits the boom and can cause some minor turbulence.
If mounted below, you don't get this, but your props will be lower and landing gear closer in to avoid them. This means that it'll take less of an "oops" for the props to strike the ground.
On a Quad/Hexa, you have a mix of Normal and Pusher props anyway, so you shouldn't need new props. You just have to have them on the right motors turning in the right directions.