Without knowing how many oher users on on the server, it is impossible to answer your question. If there are several other vbulletin users, you can bet that it won't be long before you need to move though. vBulletin is a superb feature rich forum software, but can be a bit heavy on processor resources. I seem to remember that we were evicted from our Lunar Pages VPS after we started reaching the 40 registered members regularly online with a couple of hundred or so guests, we were advised to either change forum software to a more basic one, or move, as we were too big for the VPS.
We are hosted on a couple of servers now via Asmallorange, they have always come up with the goods for us.