Allen, why your CG us important other things are equally as important.The Streak is twitchy regardless of size. Therefore, you want slow controls and a larger control horn with your pushrod in the hole furthest away from the control surface. Probably not doable now but keeping your pushrod to the innermost hole on the bellcrank would help. Your handle spacing is also important. Many times I see too large of a handle being used. You want your handle spacing line to line to be no greater than 2" apart. These methods will considerably slow the controls and limit there movement so being cautious is always important here. Working the other direction if needed. If you built the wings per plan and your uncertain of the CG, balance the plane where the forward leadout exits. This will more than likely have you in a nose heavy condition.
A Cox Black Widow would fly nicely on line length of 35' center to center. You could go out another 1-1.5 feet but windy days can impact longer length lines. Your prop choice is also going to impact your speed and how your plane responds. If your capable of flying lazy eights, this can certainly take away the dizziness as you can stand in one position and let the plane fly out in front of you. Ken