I'm running 10.13 on a MacBook Pro 13" 2009 with 8GB RAM and SSD. It's running better than Sierra here, but it's noticeable the longer time needed to boot up, so I imagine how it runs on older HDDs... oh, and I've installed on a new partition, not upgraded. Although it's running fast, there's some bugs with sleep — sometimes my Mac doesn't come back after sleep, and I need to force a reboot... so, keep that in mind.