Hey Beanie
I have a 400Watt electronic ballast and it runs both MH & HPS blubs.
All I have to do is change the blub and plug it in.The ballast runs cool & no noise or heat.Some of the switchable ballast have a switch you have to flip when you change blubs.With an air cool hood & a good fan you wont have any heat problems.I checked a few sites for the 600w blubs and they have both HPS & MH,but they cost about the same as the 1000 watt blubs.I have a 400 Watt GALAXY electronic ballast & a 6" air cool ECONO Reflector with both HPS & MH blubs.There in a 2'wide by 8' long by 8' high closet that I put a air condition vent in the cealing to cool the closet to around 72* to 80* all the time.I veg with the MH & switch to HPS in the flowering stage.It works for me. Hope this puts some light on things for you.