Rawhide gets GNOME Shell for all display types

Rectangular copies and fills are a win, but not by anywhere near as much as you'd expect. A modern desktop (even including Gnome 2) does a lot of work that typically isn't usefully accelerated on older GPUs. Doing that in software on video memory limits you to the bandwidth available over whatever bus the GPU is on, which is going to be massively less than your system memory bandwidth. Using an unaccelerated shadow framebuffer is often faster even if you're only doing 2D.