Stop watch, data, etc., I will always go light and as aero as possible. I do not care what the figures say, in my mind light and aero is faster so I go light and aero.
if I was the op, I would try to borrow a set of light wheels and see how that impacted their performance.
When we raced the tandem TT nationals back in the early 90's we used aero bars up front, a full discs in the rear and a 50mm deep front rim. We also wore skinsuits and aero helmets. We finished 3rd in our age group.
When my daughter decided to start racing, I told her if she wanted to go fast she had to go fast. If you want to average 16mph then you need to be able to ride 18mph for several minutes. Intervals are the way to get faster. However a light bike is still more fun to ride. We went from a 40 pound bike to a 27 pound bike and it is much more fun to ride. We have each lost weight which also helps.
Wayne