I used to do what you are about to try. It was an adventure and I eventual stopped. More frustration than the tiny bit of additional throughput is worth. Here is a list of things that I discovered:
Thanks, Morris. I didn't know that clients also need to monitor DFS channels and envision the impact of being forced to switch to the 2.4 GHz band.
Based on what I've seen today, I plan to let the router remain on Channel 40 for now. It's been remarkably stable even though the number of military aircraft has increased since I posted this morning. If it remains so, I'll likely just set the router to Channel 40 at an 80 MHz bandwidth without using DFS channels and consider it a win. I'll feel pretty stupid if enabling 802.11ax/ac Beamforming was all I needed to change. But I'm thankful for the help I've received here as otherwise I would have stayed at a 40 MHz bandwidth for no good reason.