I wouldn't say it robs power it just doesnt turn up as much as you like lol. In most sport models everyone really raved about the 6.3x4 when the .074 were popular. Before that everyone tried the APC 7x3 but wasnt happy with the power. Now if you have the .074 on a light weight 1/2A plane the 6x4 will be better and a 5.7x3 repitched to a 5.7x5 works well also