For the current goals, just about anything from all VHOs to 250W MH will do.
However, if you really think SPS ( in particular Acropora ) are in your future, 175W MH isn't a good long term solution and you would probably upgrade at some point again anyway. You would be better served with the 250W MH.
If this were my tank, I personally would go with all VHOs on Icecap ballasts. You can always add MH when the time comes for sps/acropora at some point without really wasting any money as you can always use the VHOs for actinic supplmentation and dawn/dusk. Also, worst case scenerio you scrap entirely and go with a different setup, Icecap flourescent ballast have very good resale so your not going to be out a whole lot either way.
Choice is yours really, if you have a local reef club I highly encourage getting involved. Being able to see many tanks and everyone does things slightly different gives experiences that really trumps any bulletin board especially when it comes to lighting.