The best you will get is actual configurations that work with the particular usage scenarios of the person reporting. You’ve told us nothing about the factors that could have order of magnitude effects on the system load, like transcoiding, conferencing, channel driver types, etc.
Whilst my only experience is with, small, development rigs, I’ve never seen anyone attempt to give a definitive answer to such questions.
However, 2,000 Erlangs is a heavy load, and you may need to use multiple machines, with load balancing proxies.
Remember that each call requires a process and about half a dozen file descriptors.
Also, although I’m not sure if it is still true, the code that handles parking uses the select system call, which is limited to 1024 file descriptors, so you should check whether than has changed before considering parking calls.