Just thought I'd pass along my experience after almost 24 hours in with 10.13 PB2 on my iMac late 2014 5K with 1.12TB Fusion drive, 8GBs RAM and I'm very happy with the results -much better than previous 10.13 betas. Everything was backed up to iCloud, a Time Capsule and a spare external drive before downloading and installing 10.13 with APFS conversion enabled for install over my primary partition since testing it on a separate partition was too laggy even when choosing HFS plus. (I'm not sure if this true but I read in the ASC when creating new partitions on a fusion drive, the new partition is relegated to the platter drive only which would explain the degradation in speed.) I'm also happy to report no more folders with question marks indicating my start up disk can't be found with PB2/APFS that I experienced every morning when waking the machine using PB1 and DP1. I'm also experiencing very little lag (1 to 2 seconds) when opening standard or core apps like Pages, Numbers, Safari, Disk Utility,Photos, etc. though it took two hours for system processes to settle down. Here's hoping my positive experience continues through next week.