None of the links on the XF forum on your site seem to work. They take me to the wrong page.....
I think your idea is basically good - maybe a resource could eventually be put together and handed off to Jake or another developer to post in the RM here.....
For starters, it would be good to set maybe 3 examples, one for a very small forum (never more than 100 users on it and less than 100K posts), a medium forum (up to 400 users at one time, and maybe 1,000,000 posts) and a very large forum (1,000+ users at one time and over 2 million posts).
We could even do just the smaller two since most folks using a very big example know what they are doing.....
My own forum is maybe 700 max users at one time, 1.2 million posts and 22,000 members.
It runs on a dedicated server Quad Core 2.6 Xenon with 8 Gig RAM.
APC and memcache are optional extras - my guess is that if it's not fast without them, they alone won't make the diff.
More important are the resources you devote to mysql and apache (or your choice of web server), as well as whether you use the ES search add-on.
I would not want to be running my setup on a server with less RAM...or even with less of a CPU. My guess is that if I peak at 1,000 users (which would probably mean 25,000+ page views per day), I'll start to see slowdowns. Right now I am at 18,000.