RE: Brison 6.4 prop selection
Try a Biela 28-10. Another choice would be the MSC 26-10. The MSC REALLY loads the 6.4 down. To a point that's about 600 rpm less than the Menz 27-10. The Menz at around 6,000rpm, the MSC at 5,400 rpm +/- a little. The Biela should be between the MSC and the Menz.