Resurrecting the defunct .351 SL, upping the pressure and dropping bullet weight doesn't sound very legendary, since game laws are the only real reason for it existing.
Better options for low recoil rounds if you aren't mandated with sillyness.
222's and 223's kill deer sized stuff all day long, many in trim packages.
I have shot and seen shot deer with fast 22s. I am not impressed. Of the deer I have seen killed with only one shot was a head shot and heart shot. The heart shot deer kept walking like nothing happened until it fell over. 2 season ago my son shot his first deer with a .223. 4 rounds later, all of which should have been killing shots, the deer finally just fell over. Little internal damage and lacked penetration. I have yet to see a deer shot from a bigger diameter bullet act the same way or have the same erratic results.
Having said that I am willing to try the 52g TSX in the .223 if something else doesn't work out.
As you noted, BULLETS! I've had quartering pass throughs on hogs with the TSX, while obvious varmint class .224 bullets fail, since they were made to fly apart. Lacking penetration lands squarely on the bullet design.
I'd take a 222 class cartridge with a bullet that digs WAY before buying some niche, expensive goofball creation that will penetrate less than a stellar .224 bullet.
Practice with the 222 class is on the cheap as well, if you are inclined.
