That looks great. I've ordered one of the Speedledge units to try. I use a CR Speed WSM II for both my M&P limited and open guns. I think it will work with a thumb rest just fine.
I think the eyebox is way too critical, at least for me. I will be returning mine under their warranty program. I wish there was someway to quantify "eyebox".
Has your FS steel gun been finished? And if so, how does it run? I'm also curious what others would recommend for a platform to make 9mm major, FS or 9L. I'm guessing that the 9L has to have the slide lightened, does the FS?
Barney