Powerbelts = pure lead= old technology = not neccesarily bad
Sabots = lots of options = new technology = better terminal performance over a wider range of velocities.
If you push pure lead too fast, it will come apart. Powerbelts seems to be made from pretty soft lead so they are OK up to moderate velocities if you use a big enough bullet.
sabots choices: many of the same choices as modern rifle choices (nosler partition, barnes, etc)
That said, I have never shot sabots, and shot powerbelts for many years until what I feel are better conicals came along. Namely 1) Thors (a pure copper barnes bullet) and 2) Hornay FPBs (lead alloy bullet harder than pure lead)
For sure with powerbelts, you need to keep your velocity down (prob in the neghborhood of 90-100 gr of powder) and the size of the bullet up (295 should be fine for deer). If you want to push the velocity and still have the bullet stay together when it hits an animal, go with better built sabots or Thor conicals
Which also brings up another point. 100 grains of black powder equivalent is plenty of power to kill any north american game. Don't buy into the "magnum" mentality that says shoot 150 gr. 100 gr is cheaper, easier on your shoulder (which makes me more accurate), and has plenty of power. My elk load is 95 gr of BH 209 with a 350 gr Hornady FPB.
I also think I have heard people say sabots are cheaper to shoot.