Interesting. I've always heard that we cannot really perceive a difference less than 2x, so upgrading before then is just a waste (ie 8 to 16GB RAM, or 2K to 4K screens, or 30 Hz to 60Hz, or a doubling of CPU power, which is why Moore's law focuses on that metric), so I'm curious how this 4x metric translates to real world product cycles.
From Geekbench:
M1 MBA Single Core: 2343
M4 (from this article: 3864
1.65x improvement: Indicates upgrading from an M1 to M4 is not recommended.
I replaced my 2015 Macbook Pro Retina with an M2 15" Air.
1174 vs 2595
2.2x improvement: At least is a perceptible difference (>100%) but nowhere near 4x improvement
The 2015 notebook was fast enough, and had tons of memory and storage, so I could have held out for a few more years, but the screen failed. I don't replace my devices frequently, if they still work (I am using an Iphone 8!) but I think technology products simply aren't made well enough to last until a new model is 4x faster than the old one.
I would
target a 2x to 3x increase in specs before you upgrade--with an absolute minimum of 2x. But
I don't see how you can practically hold out for a 4x (maybe with desktops you can, if you upgraded them with RAM and storage so they will work longer).
Looking at Geekbench, you have to go back about 10 years to find a Mac with single core scores 1/4 of the current M4. Non-desktop hardware made these days just won't last that long. (I am far more careful opening and closing my Macbook lid as the screen is probably the first part to fail).
Looking at phones:
Iphone 8: 1033
Iphone 16Pro 3391
That's only a 3x improvement and it's hard to still run an Iphone 8 today!