I've only ever used one in a Mac at high school. This was the beginning of the end for Motorola 68k because of the heating problems?
How big was the difference on the Next between a 68030@25 and the 68040?
I know that the FPU was on the chip so maybe there was no delay when accessing the FPU instruction set during the program.
Also the 4K CACHE (Data/Instruction) increase over the 68030 of 256 bytes is a big increase.
What about noise? I read that the 68040 put out a lot of heat so noisy fans.
This article states a 2.5 to 300% increase in performance
https://lowendmac.com/2014/cpus-motorola-68040/ on Macs. I know Steve Jobs NeXT sent out a letter touting a 400% increase in performance perhaps inclusive of faster chips on th motherboard and optimization of the NeXTSTEP software.