I couldn't find recent summarized data for the (excellent) benchmarks provided via the sd-extension-system-info repo, so I went ahead and pulled/summarized it. Here is the median It/s for each GPU with more than 10 entries in the table (single GPU setups only).
Source: https://vladmandic.github.io/sd-extension-system-info/pages/benchmark.html
Note: updated (found an error in the original post where I hadn't actually eliminated dual GPUs etc.)
Oh, I just realized I posted a version where I hadn't filtered out dual GPU setups. There's some weird data in there.... that's a dual GPU one. Here's the actual single GPU only (the "x2" was for dual GPU stuff in the original post).
Much thanks, still a little confusing if you ask me. I thought it would have exponential increase proportional to the Vram.