I assembled my components over a long period of time, so I've got some old school 400w MH ballasts and a couple of 600w digitals, + various cheap LED panels. I've run lizard lights with HPS and gotten great results.
Mixed spectrum provides the best results for me, but it's more like "mixed gear" and the spectrum a side effect.
I recently put some seedlings and a couple of donated plants under a bare bulb 400w MH and they did *not* like it! Probably the UV. I switched back to HPS and they are doing much better.
BTW what happens to spectrum if you drive them below max voltage? A buddy gave me a reflector that had a 1,000w EYE hortilux HPS bulb in it. I'm sure the output is diminished because he ran it for at least a year. All I've got is a 600w digital ballast to drive it. I'm running at the highest setting -- "600w boost".