Another factor to consider is how you will keep your SMTP ip-addresses from being blacklisted. Companies like Mailchimp and Sendgrid spend a lot of time and effort on this. With your own very low volume, it takes only a couple of persons to mark your email as spam and suddenly all mails sent from your domain end up in in spam folders, no matter what DKIM or SPF settings you have configured.
Only reason I would see is when you want to keep your email away from the NSA and therefore out of the USA (Fastmail is Australian based btw http://thenextweb.com/insider/2013/10/07/are-overseas-based-...). Keeping your server out of the USA will not mean that your email will never travel through the USA, where the NSA can still access it, as SMTP is very cleartext between MTA's.