> a 5x speedup [...] I also wonder if you'd even bother writing code to do it on the GPU in the first place
A 5x speed-up is very significant in many applications! I've spent a bunch of energy on several projects just aiming for a 2x speed-up on GPUs - battling against SIMD and other optimisations on the CPU side.
As for real-world examples: The tensforflow.js CPU back-end runs something like 10x slower than the WebGL back-end, and I've got some great mileage out of the CPU back-end in simple node.js apps that don't have a GPU attached to their server.
A 5x speed-up is very significant in many applications! I've spent a bunch of energy on several projects just aiming for a 2x speed-up on GPUs - battling against SIMD and other optimisations on the CPU side.
As for real-world examples: The tensforflow.js CPU back-end runs something like 10x slower than the WebGL back-end, and I've got some great mileage out of the CPU back-end in simple node.js apps that don't have a GPU attached to their server.