My 1515 2.5d works really well on 6s flightpower 25c 4900's in my e-maxx and now truggy, and it doesn't even overwork the quark. Low 40's will be easy, even on 100f + days like I've used it in. The highest I've geared it is 11.63:1 with standard size truggy tires and didn't have problems.