Mikey,
Go with 14x7, up to even 15x8 and it'll make it come alive more. The X40 can handle 4S IF you get a separate BEC for it. 13x6.5 on the 10XL is a 4S prop.
Charles,
I think on most of my tumbles I'm at 1/2 to 3/4 throttle. Downline WFO is definitely a no no for me
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