Your understanding of the situation is quite good. Last time I checked, HUD code dwellings specify 1 1/2 for clothes washers. Not long ago, I was called to a house built in 1967 in which the washing machine drain would overflow occasionally. None of my snakes would go through so the wall was opened and the trap was a very deep cast iron unit. Removed it and discovered that the interior was flawed with casting flash due to a bad sand core. The bend in the trap was sharper than those shown at the link. Replaced as much of the drain with 1 1/2" PVC as could be accessed from that room. They have reported no more problems.
Your decisions, your responsibility .

Here is a link that might be useful: Cast trap

Hmmm, it seems 2" is standard for code from what others have written/said. I'm willing to chance it and add a 2" if there are problems, but just was hoping someone could give me a really good reason to not even risk it. Since it's worked since 1983, I just can't see how it could be any different with the other drain, but am willing to listen.

Thank you for your response!

The problem was that older style washers would empty a lot of water very quickly and a 2" drain prevented backups.

I have a frontloader on a 1.5" drain for 7 years and it's fine.

I understand not everyone who comes after me will have a front loader as well as code / inspection issues. That's not really a concern here.

Thank you, Jake. That's what I'm thinking, too. If it works downstairs and has since 1983, why wouldn't it work in this new space? It will be a huge $ saver if I don't have to install a new drain.

Hi, If you have enough room install a deep sink and drain the water from the washer into the sink. The sink will act as a buffer for any excess water the pipe can't handle and you would also have a handy deep sink to use for other projects.
Woodbutcher

Thanks, Woodbutcher, that's a good solution, but this is going to be in an upstairs area kind of open to the bedroom (I'll put it all behind closet doors) so I don't think I want a sink there and do have a nice utility sink in the current downstairs utility room.

I would use the 1-1/2". When I redid my basement, I used the slop sink solution and do not like it. With HE appliances, very little water is used. It will be able to handle the flow.

Thanks for weighing in, Mayflower. I'm inclined to try to use it.