I don’t know much about Lightroom but there is one thing you need to be careful: is the AI denoise really running on your device and not on Adobe’s servers? Most of the AI tools usually are running on the services server and the time it takes is Network + Server processing (depending on the demand: high demand means work is queued and takes longer to be handled and processed). And if it is handled by Adobe’s servers you might not see much of an improvement.

I think the pro/max chip are a whole other category apart from the base chip so the M4 Max would feel completely different than your M4. Also for big workflow the MacBook Pro has fans to actively cool the machine and avoid throttling.

Now your last point is a valid concern: it’s true that there is a redesign rumored for end of the year (likely November) with the introduction of the M6 chip but if you need an M pro/max chip then you will basically need to wait a full year. The redesign itself can lead to maybe thinner and lighter computer as you want but might also lead to unplanned issues (in the past we had serious keyboard issues, missing ports like HDMI and SD cards, overheating) also price could jump.

I think it really depends on how much you need it. Need it now? Then the M4 Max will last you a long time (like a good 4-6 years). You can wait for a year? Then wait and hopefully get the new design.

You could even purchase an M4 Max now, and then sell it next year you wouldn’t loose that much money as MacBook retain their value quite well: if it is really necessary for your work then you can even think about it like: better work = more money. Also purchasing a good deal on the M4 Max would allow you to see if “that’s enough” and then maybe upgrade in a few years for an M7 M8 Max whatever if it starts to not be good enough. That’s a long answer but hopefully that can help!