My corrections are in the 4.x range, minus I think. I've worn progressives for a couple of decades -- as a kid I word bifocals and I really got tired of dumbasses telling me my glasses were cracked, as if
1) both lenses would crack in a straight line in the same place
2) I wouldn't have noticed
For the first few days the parallax / shifting was really disorienting, but I quickly got used to them.
One respondent above describes bifocals as having hemicircles -- I've never seen those, only the transition in a straight line all the way across.
Due to shitty eye coverage @ my previous employer, my current glasses pretty much had to come from Lenscrafters. There I paid extra for some fancy progression shape, I forget what they called it. I find that I unconsciously tilt my head up/down to get the right spot for a given focal distance.
I've given up on contacts -- pain in the butt, could only tolerate them for a few hours really, and they didn't stop my left eye from crossing the way that glasses can.
The biggest issue I have with lenses is that it seems to be nearly impossible to get them without an antiglare coating, aka smudge-magnet, especially with any but the lowest index material.