I get it, I once gave a prize-winning negative to a co-worker because he wanted an example to try to match, and I never got it back.
Frames 17 and 26 show sufficient density in the highlights. This tells me you developed the film enough. But the frames you printed are thin. I think it's the scene lighting (flat light in the first place). So the advice to develop longer... would apply... if you get into the same situation again with the same kind of dull light. Otherwise, it's OK to stick with your current developing plan.
Your print #1 looks pretty good to me. Since it was done on a Condenser enlarger, you would need to use a higher grade to get the same look from your C760.
For the next print experiments, don't be afraid to overshoot and give filtration for Grades 4 and 5. At least then you'll know you went too far.