Miralax is awesome isn't it? I had one kitty on that for a while. I did have to raise the amount over time to get the same effect, but still way way less than Lactulose, which never worked great for him anyhow.
When I switched to free-feeding a couple of mine did go nutso and pork out at first, but after a while when they realized the food was really there to stay, they mellowed out about it. Not that I'm advocating you switch to free-feeding just sharing in case it's somthing you want to do but are worried about. And of course ECID on how they would react to a change like that.
I don't have any high dose experience so don't feel comfortable commenting at all on that aspect, but it's nice to see some pretty blues in the spreadsheet!