Flameproof suit donned. Please correct me because I'm pretty ignorant about modern hardware. My main interest is playing lots of tracks live in Logic Pro.
On the variants: An M1 Max is 10 CPU cores with 8 power and 2 efficiency cores.
M4 Max is 16 cores, 12 + 4. So each power core is 50% faster, but it also has 50% more of them. Add in twice as many efficiency cores, that are also faster for less power, plus more memory bandwidth, and it snowballs together.
One nice pseudo-feature of the M1 is that the thermal design of the current MacBook Pro really hasn't changed since then. It was designed with a few generations of headroom in mind, but that means it's very, very hard to make the fans spin on a 16" M1 Max. You have to utilize all CPU/GPU/NPU cores together to even make them move, while an M3 Max is easier to make (slightly) audible.
I routinely get my M1 fans spinning from compiling big projects. You don’t have to get the GPU involved, but when you do it definitely goes up a notch.
I read so much about the M1 Pros being completely silent that I thought something was wrong with mine at first. Nope, it just turns out that most people don’t use the CPU long enough for the fans to kick in. There’s a decent thermal capacity buffer in the system before they ramp up.
The M3 is much more typical behavior, but I guess it's just dumping more watts into the same thermal mass...
The M1s are likely to remain pretty usable machines for a few years yet, assuming your workload has not or does not significantly change.
But if the M1 isn't the bottleneck, no reason to upgrade.