That's why I said "right now", since I feel that most people have moved from the one you linked to AUTOMATIC's fork by now. hlky's fork (the one you linked) was by far the most popular one until a couple of weeks ago, but some problems with the main developer's attitude and a never-ending migration from Gradio to Streamlit filled with issues made it lose its popularity.
AUTOMATIC has the attention of most devs nowadays. When you see any new ideas come up, they usually appear in AUTOMATIC's fork first.
Just as another point of reference. I followed the windows install. I'm running this on my 1060 with 6GB memory. With no setting changes takes about 10 seconds to generate an image. I often run with sampling steps up to 50 and that takes about 40 seconds to generate an image.
They sure do. InvokeAI is a fork of the original repo CompVis/stable-diffusion and thus shares its fork counter. Those 4.1k forks are coming from CompVis/stable-diffusion, not InvokeAI.
Meanwhile AUTOMATIC1111/stable-diffusion-webui is not a fork itself, and has 511 forks.
This is by far the most popular and active right now: https://github.com/AUTOMATIC1111/stable-diffusion-webui