I have mountain horse paddock style boots and they are so warm. I got them last winter and they've held up nicely. I know all about bad circulation, I have reynauds disease so it's really hard for me to do anything outside in the winter and still be able to use my hands and my feet get pretty bad too. I go for two pairs of socks and these boots I have, they mostly do the trick.
I've yet to find anything that helps my hands so that's what usually dictates if I ride or not.
I have the Mountain Horse Ice high rider and my 7yr old has the Rimfrost Rider.
The Rimfrost riders are VERY clunky and not as nice or warm as the Ice high riders. They're fine for a once a week, hour lesson and head for home use.
The Ice high riders are very nice, I am practically living in mine and yet to have cold feet. I managed to dump water in them when filling buckets and I didn't even realize I had wet feet until I got home. I am wearing the thickest SmartWool socks with them though, I need the extra warmth and because I have very thin calves, the thickness of the socks to fill up the boots.
I'm really against instant warming packs, personally. I heard a horror story at a barn I used to ride at where a girl put them in her gloves, and one glove lit ON FIRE. She had to take the glove off, throw it into the woods and get off to stamp out the flames. She got 3rd degree burns... Ever since I've been really afraid to use them, even though I have a bunch of packs.
This is the first time in history I've heard of something like this happening although I'm sure it's not the first time it's ever happened. That being said - this is one of those things you have to chalk up to whether or not you're willing to take the associated risk. In -40, no boot is going to fix your issues. The toe warmers I use are "Little Hotties" - I swear by them. So to keep my feet warm in ridiculously low temperatures, I'm willing to take the risk that my boot is going to catch on fire as the odds of hurting myself in a bath tub are probably higher than the aforementioned experience/story.
I should mention too though that the glove packs are WAY different then the toe inserts (for me I use the same brand of both). I can see having issues with the glove packs as even mine I can only leave in until I bring my mare out of the field - and at that point the packs are so hot I shove them in my pockets until I'm done my ride. I've never had an issue with the toe inserts to the point where I said to myself "this is way too hot". I was to scrap either - I'd scrap the glove warmers and just wear a thicker insulated glove.
I have the Ariat Bromont lace up paddock boots and love them. I use them for barn chores and riding, and even a year later they've held up beautifully. I can walk through fairly good sized puddles and still have dry, warm feet :).
I would also recommend the Stella Polaris Mountain Horse boots. I got a pair because my feet get to the verge of frostbitten when I ride in regular boots, no matter how many pairs of socks I wear. These boots have the faux fur allll the way in the boot, even in the foot. I've been okay when it's been 27F with a windchill of 10F. Much colder and I'll have to think about a thicker pair of socks, but the zipper on the mountain horse boots tends to be more durable than others, and the Stella Polaris has an elastic band that goes down the side that makes calf fit a dreaaaaaammmmmm. :) I plan on having them for years, and if you buy stuff at Dover, they have an amazing return program, so any damage and they'll give you a refund or a new pair. We've been told at the nearby Dover store that people come in with new stuff and rediculously abused things, and can still return them. So I think they are worth saving up for.