If you're going to merge those two, also merge in my other canonical question:
How do you do Load Testing and Capacity Planning for Databases
However, I think that both (all three) have a place, and could all be displayed.
If they are merged, in the spirit of being a resource for Professionals, let the opening be "We are not going to help you with your Capacity Planning and Load Testing. Here's Why: (answer regarding your special snowflake goes here)." Then, "However to be helpful, here are some thoughts we've put together on how to go about it." And possibly links to the "Web Operations" and "Art of Capacity Planning" books.