Nvidia GTX 1660 Super with 6GB of VRAM.
I do runs at 384px by 384px, with batch size of 1. Sampling method has almost no impact on memory. Using k_euler with 30 steps renders an image in 10 to 20 seconds. The biggest thing that affect rending speed is the steps and the resolution, so 512x512 with C 50 using ddim is much slower than 256x256 with C 25 using k_euler.
The sampling methods run mostly in the same timelines, but the k_euler one can produce viable output at lower C values, meaning it is faster than the rest.
Don't add gfpgan in the same pipeline, as it takes more vram.
I'm running it on Windows 10 with latest drivers. I set the python process to Realtime priority in task manager (makes a slight difference!). Have not tried it on Linux.