Consider that stall speed increases with increased wing loading.

As you ran out of runway before being able to lift off, you are correct to try a longer, lower pitched prop. It would be helpful to find a review of that engine, to see what prop gave the most thrust and start from there. You will arrive at the max speed for that prop the quickest. If that speed is not enough, go for the one with next highest thrust, which will most likely be one with higher pitch or RPM.

Ken, AMA 19352