Well, if we believe Fred Weik's formula, the difference at 100 MPH is effectively zero. Probably an advantage for the direct drive installation after we subtract the friction losses for the belt drive.What's the thrust difference at say, 30 mph? What's the difference at 100 mph?
Difference at 30 mph? Dunno. Prop efficiencies at speeds that low are apparently tricky to model, so we'd need to test. But it's a sure bet that the bigger fan will do better at low speeds.
The trikes, UL aircraft, and other kites are using redrives, which makes sense for their airspeed regime.
The OP says he's going to fit this engine to something similar to a DA-11. That plane stalled at 60MPH and probably climbed out at 90 MPH, cruised at a claimed 125 MPH. That doesn't sound like a project that needs a PSRU, and Leeon didn't use one.