Okay. Mike. I would find a good, solid, and reliable registrar with decent DNS services. It is not necessary that they are local to your server and here is why.
When a user makes a request, it is their ISP DNS that they hit, not yours. Sorta.
Essentially, your DNS records will get cached, propagated, and otherwise distributed according to what any ISP DNS wants to do. When a user requests a domain name from their network, let's assume that has never happened before, the ISP DNS will look-up your domain name and match it to an IP address. It would be easy for us to think that would be the registrars DNS, but not necessarily. Most of the time, if an ISP DNS does not have the answer, it will query the networks up-stream DNS and so on. This, of course, is not always the case, but generally the case with ISPs.
For example, I am using CenturyLink. In theory, if I am a dumb user, then my router is using the CenturyLink DNS servers. If the CenturyLink DNS does not have the answer, then it queries the Quest DNS. CenturyLink should be fast enough, however, Quest will be much faster. In fact, much faster than many registrars.
Many ISPs have DNS caches. Think about my example for a bit. Quest is a major telecom with a significant backbone. It is very likely that Quest will have had the domain name requested at some point whether the record is fresh or not. Since some ISPs do not care too much if the record is fresh, it will serve what is either in the DNS or DNS cache. Even if the ISP wants to refresh the record and queries the SOA which is likely with the registrar, using my example, it is a DNS on a backbone that is making the request.
So while your registrar is not often hit, as long as they are fast and have a good proximity to a fast network, that should be fine. This is why for some, GoDaddy works well. If performance does become an issue, just chose a fast registrar on a fast network or even a DNS service on a fast network. The closer to a backbone the better. This is why larger registrars work as well as they do. They are well located.
Keep in mind that even a tiny network in a tiny town can have immediate access to a backbone. I do and I live up in the mountains.
I may not have explained this perfectly. I had to rush because I have some place I have to get to. However, you get the point that the registrars DNS is the least often DNS hit to locate your IP address.