In my current grow, I started under 4 cool florescents for 3 weeks, then bought my 150w HPS and put them under it for the next 2 weeks of vegging. The HPS outperformed the tubes in the same area. More lumens definitely helped in my case, but I am sure that plants grow fine under HPS for all stages. I have used MH for vegging with great results as well, but MH isn't great for flowering. Using both during flowering increases lumens which increases yield, especially if you use the MH to get light to areas that the HPS isn't penetrating to. I know this isn't very scientific evidence for you, but that's what I have observed myself. Hope it helps.
TicTac