Break a leg? How about just taking a vacation?
There are ratios that you can find on the Internet (such as
this article ) which may help in getting a few more folks. Realize it hardly ever comes down to 'the perfect mix'. New projects come up which add more servers than you can handle, folks leave, company downsize both personnel and systems. It all comes down to what the company can afford (or what they can get away with).
I am working on the same computers since 1999 - there were approximately 150 servers when I started and 16 people (we also did user support). Then cut-backs - 150 systems, 8 people (still doing user support). Then user support came down to almost nothing. Then the company was bought out - we ended up with 4 people, 150 servers. Then we were down to 2 people. That's when they started getting rid of servers - down to 40. Also, during all this time we had 24 X 7 coverage on-call. Then the servers and SA's were 'sold' to another company - now we are at 10 sysadmins and 400+ servers (with around 25 of the original servers from 1999).
End result in my opinion - push to have at least 3 people - especially if you have to have 24X7 support.