Before looking at performance it may be wise to look at which 3-blade metal props, if any, have had vibration studies done on the IO-390. I think you may find the list of tested props is very short, thus you would end up being in uncharted waters with respect to understanding whether any RPM restrictions might apply.
The IO-390 is a fairly late-comer to the Vans aircraft but has been used extensively in the Glasair Sportsman. In that airframe there are no 3-blade metal props used with the IO-390. If you want a 3-blade then you're limited to composite props on that airframe.