Speed is important especially for the page views / impressions if you have a biz model wrapped around your site that keeps the lights on.
Be weary of running adverts on Discourse. It is problematic. Infinite school might destroy your hopes and dreams here. I have seen reported and directly almost 80% drop in report revenue in earlier 2.x version and in that case NodeBB solved the problem. Moving to the wrong platform might totally break your business model and in more ways than one!
Fast page loads and option to disable infinite scroll are not to be scoffed at by any means and are also an indication of the kind of thinking and care behind NodeBB and also the quality of what is under the hood.
Existing user bases rarely ever take kindly to new platforms and from my reading and direct experience and comparing notes, Discourse is not a well received upgrade to existing communities.
Thread very carefully here. You may loose your user base overnight and IIRC the creator of Discourse has as much advised it maybe not being for established communities. Discourse does seem orientated more toward those that have no forum presence but what to establish one.
Bottom line - A forum is nothing with users but it's easy to get distracted with the bells and whistles.
NodeBB is like a interative and adaptive evolution. I actually do not like to compare Discourse to NodeBB, Flarum is the obvious comparator, NodeBB is more out on it's own IMHO and NodeBB is more loyal to the idea and concept of a forum.
No platform is perfect, but NodeBB is great, however a godo guide is you have to find or you should look for the one you can live with, not the most features etc. etc.
I think NodeBB is in that ballpark, remember it's not just you but you and all you users have to live with it - I can not state this singular point enough.
I think NodeBB is more technically accessible from many angles and probably easier to make your own and the attitude of the founders comes through in a positive way, not always the case with other platforms.
So to end on an analogous point and I'm no car/auto buff, but if I was to compare NodeBB to a car brand I think I might say it's more Honda.
What brand of car is Discourse, that's a though one... Maybe one of the German ones, BMW perhaps, when it breaks it's a total PITA to fix and suddenly the bills start to mount.
Summary of primary points:
It is possible (others may chime in here) but it may be approx 50% cheaper to self host a NodeBB Vs a Discourse in terms of the comparative performance enjoyed.