The subdivision surface modifier seems to be extremely laggy on anything above 5k tris for my machine; as seen here, it's barely usable on the lowest settings possible on the modifier itself (1 subdivision in viewport, 0 in render, 1 quality, Use creases turned off, sharp, Catmull-Clark) as seen here: https://gyazo.com/b6ebdadacff472f47f61798706b61a60

I've tried this on a new installation of blender 2.8, on my main computer (Intel pentium g4560, rx 480, 8gb ram) and my work computer (Ryzen 5 2600x, gtx 1060, 8gb ram) and both give nearly the exact same results, even if one is clearly inferior specs-wise.

This however doesn't happen in blender 2.79; an easy quick fix for this would be to have a "legacy 2.79" option within the modifier itself, that way it's possible to work in edit mode with 2.79 performance, and then when it's time to apply it, change it to opensubdiv mode as an option.

Thank you very much for your hard work, and I hope it's fixed soon!