Ted,
The method you propose for measuring the flow will be close. The flow rate you measure will probably be a little on the high side because the panel outlet is now at zero pressure as opposed to something when it's connected on the other side of the bypass valve, but close enough. I think Carl said what I said but in simpler terms. Since your pressure only increased 2 psi with the bypass closed, that's good. Indicates little flow resistance in the panel. Even if you run that way you're toally OK. 8 psi rise? No.
Al