It doesn't matter what rpm range you *want* to see, it's what is safe for the engine. It is not always safe to pull the guts out of an engine at off-idle rpm speeds, and a pull starting at 3000-3500 and going a little past peak is all that is really needed to see what an engine is doing.
You will not load an engine any harder than it will be loaded on a dyno, and it's the same theory as hooking your truck to a heavy load, heading up a hill, and pulling the guts out of it. Trucks are made for that, but your engine, designed to make hp at 5500, 6000, 6500, and 7000 rpm are inefficient at lower rpms, and often are designed with much higher compression ratios, much quicker advance curves, and much higher DCR. It's very easy to "rattle the valves" with a full load at low rpms. Peppering the spark plugs isn't something that I would chance just to see how much power you're making at cruise rpm.
These engines are a lot different than your average "Coyote" with variable valve timing, fuel injection, etc, etc.
There's my "field day."
FWIW, if you want another opinion, I'll say that when I was loading a Boss 9 engine on Jon Kaase's dyno, the customer was present and wanted Chuck to pull it down to 2500. His reply was, "We do not like to pull them down that low."
It can also be an issue of dyno operation. Some dynos have u-joint rattle at low rpm, or are just not able to hold the engine at that rpm.