I've started using 8k maps for hair, not simple resizing though. So far I've just taken 4k maps into photoshop and quadrupled them so the details/hairs are finer. No issues with RAM so far, even my 6-year-old iMac has 32GB RAM.

What's your process for moving 4k to 8k? My other half is a graphic designer and she finds: http://waifu2x.udp.jp useful so I thought I'd try it, but it didn't seem to make any difference for me.

That eyebrow looks good btw... is that standard miki? texture or geometry or both...?

Maybe we should start a 4k versus 8k comparison thread?