I had a few games upgrade to Ren'py 8.x and the animations all became super laggy on me, even ones that played fine in older versions. They had played fine in games released on v7.x's, this even though all the graphic-heavy games I played had to have the graphics settings all at their minimums for a few years now.
Luckily for me (although not for my wallet) my old computer that I'd been nursing along for almost 10 years (the graphics card was only about 6 years old, but still) chose last winter to let me know that it was not long for the world, so I decided to finally just get a new one, making sure I had a high-end card this time.
I'm pretty happy with the result, and the smooth Ren'py animations are just the tip of the iceberg.