Re-post from a similar post that I made on Reddit:
I've been giving out 4 xp per session, with each session being about 4 hours. I then usually give a boost at the end of each adventure (6-10 xp, pending complexity). It has worked very well for us.
We are heavily on the role play, and significant parts of the adventures are usually (unplanned) interactions between npc/player, player/player, player/environment and very little spent in actual combat. With heavy roleplay (and additional scenes for backstories), the promised land took us just over 12 hours to go through (3 sessions), for a total of 18 xp (4 per session plus 6 for completion). So my promised land gave a lot more than 8 xp and took significantly more than 4 hours - but it also had more scenes, which is easy as two of my players have the arch-enemy burden.
I'm not planning on docking players xp for "slow rolling" - as long as there is plenty of role play involved and character progression, I see no reason why I would - it is all about character growth. It has happened more than once that I left the room for a quick toilet break, and when I come back, my players are still acting out their characters interactions between themselves (and not even realising I left the room for a couple of minutes)
In retrospect, I could probably have standardised on 3 xp per session and it would have been fine.