I would sail the boat first and see how it does
Alan-Why don't you sail the boat first and see what it needs. I'm sure you probably know this but there are a more fractional rigged racing boats that don't use runners than that do. They adjust the rigs for each race so that they have the proper shroud and headstay tensions for the conditions of the day. If the mast section of the 26.5 is not tapered at the top or is not too soft, a standard backstay adjuster may be all that is necessary. Also, I know you talk a lot about having a tight headstay for pointing, but unless you sail in 10kts and flat water all the time, there are plenty more situations where some (not excessive) headstay sag is very important. With a light boat and a wing keel, it is especially important to be sailing the beats as flat as possible and at max speed. And, on any boat in moderate breezes with a heavier chop, you need the power to get through the waves. So it is better and faster to foot for speed instead of getting those extra degrees of point given these conditions and variables, and that is when your headstay sag equals power. Then when the wind pipes up, you can put on the backstay for the purpose of flattening the sails and bending the mast, so the runners are not really a necessity then. You may find that you don't need them at all.By the way, are you downsizing or just getting another toy?? Just curious.