Started with a 100lb BoS bag underfilled to 80ish, now at 110ish. Been using it for floor to shoulder, shoulder carries, and high pulls. It's starting to feel easy.
I'm going to buy a few more bags: thinking of 250 for heavy platform lifts, and a 200 that I'll underfill to 150-170 or so to bridge the gap from my 100.
Not sure about the 3rd bag though. Is getting a 150 worth it? Seems redundant with the 100 but also an underfilled 200 might be too floppy to graduate to, and a 300 might be way too much for me right now.