Of course the 357/6.8 would be a better cartridge. The 6.8 has about 7 more grains of case capacity. However, it wouldn't be a straight case necked up to .357 thereby defeating the whole purpose of the 350L.
I had forgotten a couple nice features of the 350. One is that it uses .223 shellholders and two is that it doesn't need a custom sizing die - you just use a .38, 357 or Max die. For seating you can use whatever seater came with your die if you shoot regular pistol bullets.
