[Delphinus]

You should really look into pulse-start ballasts because a lot of the bulbs we use in this hobby will start easier and run better on them, since these are closer to the specs required by the lamps (with exceptions; you have to look at the specs of the lamps you wish to use to be certain; but the "majority" of the bulbs tend to be pulse-start rather than probe-start).

175W = ANSI M137
250W = ANSI M138
400W = ANSI M135

150W HQI = ANSI M80
250W HQI = ANSI M81

You can use the HQI ballasts to fire the double-ended lamps, or the standard mogul lamps. Even some mogul lamps will run best on the HQI ballasts (European bulbs in particular tend to fit this category).

And, as if this isn't enough info to digest, if you consider going pulse-start, then look into "long distance" ignitors. The standard ignitors tend to have a BTL ("ballast to lamp" distance) rating at 2 feet. If you want to remote mount the ballasts then you will want the "LR" (or "long range") ignitors (which you just have to order when you order your ballast) and those tend to be good for up to 10' or even 20' in some cases.

Just some food for thought. Pulse-start ballast will probably cost some nominal amount more up-front (like say $20 or so, I'm not sure), but it's better than finding out you need the other kind of ballast after you've already bought the one kind...