Depends. I run a community of about 600 users, on certain occasions (2 times a month) we have about 250 concurrent users online. After preparing NodeBB in the background on a second level tier DigitalOcean VPS (1CPU, 512GB RAM) which ran excellent after initial development, we decided to go online at one of those high peak events.
It was a disaster, honestly I had no experience with NodeJS before, so I didn't know what performance issues to expect. The site slowed down really fast when the first 60 visitors were online, at the time there were 100 of them, it got unuseable, so we made an emergency conference call and decided to go down, upgrade the VPS and power on again. That took 5 minutes, the rest of the event went smoothly afterwards (The community was not upset at all but rather proud of bringing a whole server to it's knees ;)).
So for reference:
We went for the 2CPU/1GB RAM option for 25$/month. That one managed 40.000 pageviews in an hour from 298 concurrent visitors (guests and members), no noticeable delay, with 79% CPU and about 80% RAM usage. I currently have three NodeBB workers enabled with Redis as a DB and nginx as reverse proxy, all over SSL (coming to think of it, that should have a performance impact aswell). SSH monitoring with top was running, too.
This might give you an impression