I am 6'6" 300 lbs, and I started with a hi float PFD. I didn't find much of a problem with range of motion, but I have a long torso and relatively short legs for my height. I didn't like swimming rapids with it, The extra floatation tended to dictate my position in the water, and it always bothered me. I switched to a 16 lb kayaker style PFD a while ago, and I like it more. I don't do a ton of big water, but my last swim was in big waves. I fell in at the crux of a steep wave and didn't surface for 3 waves after I fell in. I am pretty comfortable with that, but I am sure that a 22 lb jacket would have surfaced me quicker in that situation.
The 22 lb jacket I had was longer and the flotation down lower, so it pretty much forces you into a horizontal position. If I was knocked out, I'd prefer that, but I'd rather feel more in control of my body's position for most situations.
Now I am looking at rescue PFDs, trying to figure out which one will meet my expectations.
Wishing I was on the river instead of surfing the web...