The GPU renderer is great. If you're on a machine with a hefty GPU. If you're not throwing a bunch of bitmaps and/or bitmap effects at it. If you're not working with a lot of overlaid transparency.

If one or more of these is false, it starts slowing down the preview rendering. And not by microseconds. I have files that render the preview a little sluggishly, but still usably, with the CPU renderer, and take minutes to update with the GPU renderer.

I myself have permanently turned off the GPU renderer, as I regularly fail all three of these ifs - I'm on a laptop with an integrated GPU, and I do a lot of bitmap effects and layered transparency. But I regularly see new users asking why AI is so apocalyptically slow, and turning off the GPU renderer almost always fixes this.

The Data Recovery auto-saver is smart enough to realize when it's taking forever, and turn itself off, with a helpful little alert for the user. The GPU renderer is not. Please think about how to give it this ability.