Drew if your going to be going with managed servers then why not just go with a single processcor for now.
When your site grows to the point of needing the dual processor any good host can switch you to a dual processor box with no downtime.
My
Only because I do this for a living.
If you want to hit me up on ICQ 4433144 I'll give you specific numbers on what it can handle but there are many variables
IE:
how is apache setup
Kernel setup
etc etc etc