Hi,
After installing Asset Forge I had the same issue as some other users - the UI was extremely laggy (multiple seconds to open a menu) even after changing the options as recommended in the FAQ. I did notice that it was using 100% GPU in task manager, but without saying which GPU it was using (I'm using a laptop which has both integrated graphics, and a discrete Geforce GPU) - some searching suggests that Unity had for some reason got confused about the dual GPUs and fallen back to software rendering, which explains the slowness!
Tweaking the GPU settings to force Asset Forge to run on the Geforce didn't do anything initially, but after a reboot it's all sorted itself out and is running fairly fast now. So I don't have a problem any more :) but as a suggestion - is it possible for Asset Forge to detect when it's using the software renderer and pop up a warning in that case? Unless you happen to notice the oddness in task manager, it's not obvious what's happened other than things just being very slow - a warning might make it a lot more obvious what things to try.