Be very careful with overdrivening mercury and metal halide lamps. Unlike HPS where even in an overdriven White HPS the sodium pressure is still below atmospheric pressure (<1 bar), mercury and metal halide may explode with very violence if you overdriven them.
Well, I would still be careful! I hooked an MH lamp up to a fluorescent ballast, and it literally blew up in my face! a few people here can tell you that, they saw the pics! Which I can't find anymore!
I would run it on a HO ballast to be safe, i ruined a sylvania 100W merc trying to hot restrike it on the Ho ballast, it melted the starting resistor right off!
Wow thats Really Unfortunate....at least it wasnt one of your Good Old American mercury vapor lamps....ill hold out for some VHO lamps so i can Run the Proper Lamps on these....maybe even design my own Fixture.
So it might be overdriven. I am not an expert, so IDK xD