In the cold weather topic several people suggested I move from a backpack (I use a pheonix from timbuk2) to panniers.

I've already got a rack, so that's not an issue.

What I need to carry to work is a laptop, a pair of pants, 2 shirts, and a lunch. Possibly a jacket at some point as well.

When I get to work I need to be able to carry the panniers up two flights of stairs, probably a hundred feet, and then an elevator ride. I'll also likely be using them to transport the laptop sans clothes on the rare day I have to drive in to work (say, flat tire, or reporting to our 30 miles further away office).

So with all of THAT measely requirement, I'd also need something that's comfortable to carry, water and weatherproof (because getting to work with my work clothes soaked and muddy, or the laptop taking a bath, is not ideal), prefferably tough, and somewhat good looking, for use as say an office laptop bag.

I'm a big fan of timbuk2, and I love me some messenger bags. I've looked at their messenger style pannier, not sure how comfy that would be to use as an actual messenger. I don't have a prefference for dual/single style, or a manufacturer. Price is flexible, though I don't want to spend 5000$ on these. Probably in the 100-200 range. I'd rather pay for quality than buy cheap and replace.

I have the Ortlieb Downtown QL3 and would recommend it. If that's too small, the Ortlieb Office is roomier, but bulkier.
https://thetouringstore.com/ORTLIEB/O...ICE%20PAGE.htm

I just bought a pair of Arkel T-42 panniers for my commuter bike, and am very happy with them. Very easy to put on and take off the bike, very secure on the bike, adn easy access with a couple of sepatate pockets. They do require an optional rain cover but are very high qaulity. Arkel also has a couple commuter types otions as well.

https://www.arkel-od.com/us/all-categories.html

While you're looking, you can always bungee your backpack to the rack. This is what I do. On rainy days, I put my work clothes inside of a plastic bag before putting them in the backpack. They always come out dry, even in downpours.

Ortlieb makes wonderful, waterproof panniers. Super easy to get on and off, and for the short distance you're carrying them, the carrying straps will work well. Check the size of your laptop, though; a 15" is just that much too big for Sportspacker Plus.

Ortlieb's Back roller bags have a shoulder strap on each of them.

I have paired 2 bags together with nylon webbing,
and have the webbing to use as a as a handle too..

I have the timbuk2 tandem panniers, and they do collapse into a nice messenger-style setup, although the hooks tend to clink and the cinches tend to slap when you walk. The major shortcoming for you, though, would be that they're too small to fit a 15" laptop. I can fir my work clothes and lunch in them with room to spare, but they don't have the right dimensions or shape for easy laptop-toting.

Does cold weather include snow and slush or lots of rain? Personally I tend to move away from panniers during the winter and use either hard case panniers or a backpack. Any panniers mounted on a rear or front rack can get pretty dirty travelling in muddy or shushy conditions and although everything is washable - I can't do that easily at many destinations. So I do have 8 nice panniers with rain covers, but using the backpack keeps everything clean and saves the hassle.

I've also recently taken some Arkel mounting hardware and used it to attach a couple ABS briefcases to the resr pannier. Those are watertight and a snap to wipe down.

Um, why?

I can see contemplating panniers if the temps were climbing, but the temps are falling. Keep the load on your back (for now):

-It will help keep you warm
-Your bag is out of the 'slush zone'. Your fenders won't stop spray from passing cars and a waterproof pannier will keep your stuff dry, but then you have to carry a messy, slushy bag into your office.
-The load on your back is easier to deal with than on the bike if traction becomes sketchy.
-If you should take a tumble, the odds of your bag being the point of impact is greater hanging on the bike than on your back.

The downtown was waaaaaaay too small for me. I love my Office QL 2 (Large). If anyone wants to trade a downtown for an office, holla!.

Downtown is fine as a messenger bag replacement, but not nearly big enough for a true commute package IMHO (ie including change of clothes + lunch)

Funny. That is when I'd start wearing a backpack (in winter that is). No worry about a sweating back.

I agree. I would rather use a backpack in cold weather rather than in hot weather.

I use an Arkel Bug. It is convertible from pannier to backpack. The conversion process is quick and efficient. That way you have a pannier on the bike and a backpack to carry your stuff around while walking.

Klick Fix has a clip on seatpost mounted back pack,
just has the mount in the middle of the back on the pack.