Dave,
I did achieve good water pressure without the aid of a relief valve. I had one plumbed in prior to going with the Globe impeller. It was an adjustable needle valve that dumped excess water overboard. This was used when I had the bypass blocked off the year before. I have spent countless hours testing with a multitude of combinations of cooling setups. The one that worked the best was the one described above. It was a recommendation from Dean Nickerson. I never noticed any pressure fluctuations, not to say there weren't any.
Russ