What do Unity employees recommend for a standard PC build?

These are the minimum requirements, what that says is that it depends. It depends on what project you are working on. If it is a 2D game, then Intel Pentium or i3 processors with 4GB of RAM will be enough. But if you are working on the next AAA game, you will definitely need a i7 (or AMD's high-end zen chip once it is out) with at least 8GB of RAM and integrated graphics card will not be enough.

You can also look at the statistics. But these statistics do not include what type of project these configurations are used for.