My take on this is:

IF and I mean IFF! the thrust was exactly the same on both props and the lower RPM didn't overheat the engine I'd go with the lower RPM. My reasoning would be a larger airflow for one and the second and more important would be that the "feeling" of quicker spool up would be with the slower RPM. It takes less time to get to a lower RPM than a higher one. Also the larger prop would probably give more thrust earlier in the RPM range thus quicker pull out.

Thanks
Barry