Besides this being a good boot, and I live in the Philadelphia area, where it has gone down to below 20 degrees, the warmth also comes from wearing the correct sock. Two things to keep in mind, one is how well the sock draws moisture away from the foot. These boots do that as well. Also, how much distance you will be traveling. Smart Wool is a great choice and you can also go with a wicking sock underliner. These boots will be great for the winter and you should not have any problems with keeping your feet warm.

For short trips <1/2 hour these will keep your feet warm at 20 degrees, but for longer rides you might want to slip in a heated insole or socks. I have also found that if I wear my heated jacket liner my hands and feet stay warmer. Keep your core warm and your body can send more blood out to your extremities.

I have no experience with the TCX X-Five Plus at 20 degrees, but I have no problem in temps in the mid-30's at freeway speeds. I ride a GS, so there is very little protection at the pegs, and my feet are never cold with the X-Five Plus!

I've owned these for a while now, and I must say they are great boots. I live in the Pacific Northwest, where it doesn't get really cold (maybe down in the 30s, but pretty rare), but it is WET! These boots have kept nice and dry through it all, and on the cold days I've used some good Merino Wool socks for warmth. For me, everything has been fine.
These boots are not overly insulated though. If your are going to spend a lot of time in the COLD, I would recommend planning on extra layers or heated socks. Also, some good silicone boot sealant over the toe area might help.

These are mid-calf high and are comfortable. Make sure you wear socks that would extend above the calf to prevent chafing.

These come up to the mid point between my ankle and my knee, or the center of my shin bone. The front is higher than the back.

The TCX-X-Five Plus is a nine inch boot, with a slight decrease to the back at about 8-8.25 at the back. I find this a good touring height.

I would guess these to be about the same as your military boots. They're a mid-height boot, not as tall as a MX style, but they do have some good chin and ankle protection.
Check out the videos on REVZILLA, very helpful.

They are not super-high, one me they are midway between my ankle and knee. From the floor my size 44's measure about 11" high in the rear and 12" in the front.

I regularly wear these boots riding and find them very comfortable. I've also worn them all day at work, but I have a desk job. I haven't given them any long, urban hiking test runs. That said, they seem comfortable enough to pull it off for light duty use. But in terms of what I look for in walking / hiking shoes, these are definitely on the heavier end. They remind me of old-school hiking boots. You know... the heavy, thick-sole, ankle-supporting, rain-proof, bullet-proof, last-through-anything kind. The exact kind I stopped wearing in my early twenties because by the end of a long hiking day it was like wearing lead weights.

So... standing and walking in them for a few hours, I'd say they should be fine. But if "looking around" includes hiking up and down hills / stairs, walking 10 or more miles in a day, or otherwise really hoofing it, I'd find a light-weight pair of urban hikers and pack them along.

Recently went on a short 260 miles ride for the day. I went to a Powwow where I spent the entire day walking around. The surface was mostly grass and that may have had some affect on how it felt, but overall I would say no matter what shoe/sneaker/boot you wear, shopping with the wife is painful enough. I did enjoy stretching my feet as soon as I got home 12 hours later.

I just got these 1 week ago, and have been wearing them all day everyday. I have to walk a lot on my job and have not had any problems with my feet.

I have been wearing just these on rides and walking, I stopped packing extra shoes they are definitely comfortable enough for walking most of the day, you can almost forget they are riding boots at some points. Also they have a fairly quick break in period just a couple days and they are great.

Yes, I think you could - look, it's not going to be like wearing SLIPPERS, but I have almost fallen asleep in these boots. I have also tramped around a little bit and sometimes put them on just to take short walks for fun.

I would guess, though, that after 6 hours of walking around in them, it will feel good to take them off. But I don't think you'll be suffering too much during those 6 hours, if at all.

My one warning is, they're expensive motorcycle boots, and I feel like walking around in them too much could wear down the sole... not sure what the replacement options are yet.

Wear the RIGHT SOCKS for whatever temps you'll be riding/walking in, and it will make a difference. Get moisture-wicking socks for warm or cold, definitely.

Overall, I think you could do a lot worse for boots for this purpose.

I've worn mine every day for a week while on short rides, and I've worn them all day just walking around to break them in. No problems so far ... I might try going on a short hike this weekend to see if they can be OK even when the going gets a bit rough.