Golfers: help with shaft selection for irons

I went through the Mizuno shaft optimizer fitting, and it told me the best iron shaft for me was the project x 5.0. So, I started looking at irons, and the ones I like the best come with project x flighted 95 shafts. The equivalent flex in these to the regular project x 5.0 is 5.5. I managed to get a demo set, but the shafts were 6.0 flex in the flighted 95 shafts. I played with them today, and hit the ball great. I feel like I could go with the 6.0 flex and be happy. So, now I don't know what to do. Does anyone of our resident pros/experts have a suggestion? I'm leaning towards the 6.0 since it felt good today. I also feel like my dispersion would be better with the stiffer flex. What would be the downside to 6.0? What about the upside to 5.5?