I would say the answer to your last question is "yes". As for what length to start with; full length. If you want to use a light 125 gr point they will have to be full length or very close to it. If you're willing to work up to 175gr points, you may be able to cut some off. Just do it in very small increments. Once you get close to the right length, 1/4" will make a huge difference.
Also, don't forget that a bareshaft requires a perfect release, which most of us don't do 100% of the time. Don't judge your results on a single arrow. Shoot at least 10 times with the bareshaft and fletched and keep track of where each shot hits. Throw out the results of the shots that are out of the group and look at the balance of the shots to make a determination of stiff/weak.