A friend who is a highly educated engineer and well known C/L flyer since the 50's has built a 75" Lystrander with a Enya 91 for power. Yeah, it's big. He calculated based on speed, weight, etc, that line pull at full throttle to be about 13 lbs.
Anyway, there are a myriad of factors that determine line pull. This was mentioned already. Speed, c/g, rudder offset, leadout position, plane weight, thrust offset, etc. Just build it and fly it. If it's uncomfortable then sell it.