Actually, yer matching socket to bulb, not ballast.

You really do want a 5k pulse socket, and just about every HID bulb I've ever seen is a " mogul base"- the packaging on the bulb will state.

There's a really signifigant surge associated with arc ignition of an HID bulb ( sorta like the startup pull of an electric motor, but I think that that's considered an inductive as opposed to conductive surge, and I've seen differant ratings for the two types of surge- is there an electrician in the house?), so you really do need the heavy conductors even on a low wattage system, and make sure that everything on the high voltage side of the transformer is nice and tidy. Good practice anyway.

If yer worried about getting the right thing, you can walk i and buy the socket cash @ Home Depot.