1. When I start a slideshow of let's say 200 photos, LR5 takes a long time to prepare the previews. I used to run slideshows of 3000 photos in LR4 without having to wait 20 minutes for LR to prepare the previews. Building 1:1 previews did not speed this up.
2. Also when a slideshow is running, I cannot use the right and left cursor keys to move one photo back or forward.
I'm running the latest version of LR and tried this with a catalogue with only 500 photos in it as well as with one that has several thousand photos. The smaller catalogue shows the same problems.