I'm hoping the MGM barrel, a decent charge of 209, and an MMP sabot coupled with a good 357 hunting bullet will meet my criteria
It wont. You will likely have a really hard time even loading that sabot in a MGM 45 barrel. Ive been shooting 45 almost exclusively for ages. Everything from fast twist 1-20s to 1-30s and the only way ive got 45x35 to shoot is with much milder charges and bullets like the Hornady 9mm 147gr XTP. PR's Dead Center being about the only thing ive seen shoot well fast.
But if you must try, go to Precision Rifle Bullet. Get their 45x357 sabot and then get some of the new 350 (.355) Legend bullets. You will find out real quick when you try to load one. PR loads those sabots with bullets a tad smaller than .357. Ive shot them all and not a single combination would shoot as well as a 45x40 200gr SST. The only thing ive seen shoot worth a hill of beans in 45x357 are the PR Dead Centers. So if you like spending $1.50 a shot for a lead bullet its worth trying too.
You can just as easily shoot lighter 40cals like the 180gr XTP or Barnes 155gr XPB/TAC-XP and achieve the FPS you wish with a far better chance of them shooting well.
PR sabot made by MMP
https://www.prbullet.com/shop/produc....php?sSKU=0500
175gr Dead Center
https://www.prbullet.com/shop/produc....php?sSKU=0001
Bullets (.355) for 350 Legend
https://www.midwayusa.com/bullets/br...ctedSort=False