I've been using the 256x256 HD Rivershavewings notebook, and it does take a remarkably long time, but it's a more resource-intensive process than VQGAN. I'm pretty sure a less resource-intensive notebook using the same underlying architecture would produce much less accurate results. I find the diffusion notebook more than worth the wait, honestly; I've gotten some incredible results using it. 256x256 is definitely small, but I upscale my outputs using an ESRGAN notebook by @jotakrevs. Successful prompt engineering for diffusion is different than for VQGAN+Clip, too. Just by feel alone, I'd say VQGAN feels more like sculpting with words/poetry and Diffusion feels more like building/architecture. I don't know if that makes sense.