Most boards are within a few percent of one another.
There are speed differences, but they are fairly minor. It's the combination that counts. As you'll see from the tables below, the best board with one CPU can be quite a poor choice with another. Usually, when there is a wave of change through the industry, we buy samples of all the new CPUs and motherboards we're interested in and get to know them. We run them in the workshop for a few days, try them out in the staff and office computers, do some performance testing, and generally get the feel of them.