I have the same tank and use (2) 175 watt Iwasaki 15k bulbs. I keep SPS in the top half and various LPS in the bottom. I still need to find shady spots for my chalices. It'll be fine for what you want to do IMO.
I think you are getting good advice here Erik. I've been keeping corals under 250 W MH in a 120 for quite some time. Make sure you get the appropriate ballast for the Radium bulbs (Pulse Start..blue wave IIRC) they will give MUCH better PAR and color with the ballast they are designed for.
A friend of mine ran 2 250 radiums on his 120 and it was a GORGEOUS sps display with chalices, zoas, everything. I would say those lights are PERFECT for your tank. I wouldn't buy anything else!
I didn't know different ballast perform better with different bulbs. I thought itwas just with de, and se. I'd like to know more on this matter if you have a moment Henrey.
Check out Dr. Sanjay Joshi's reef lighting guide. He's considered my most to be a guru of halide lighting. Manhattan Reefs - Sanjay's Lighting Guide You can just plug in lamp and ballast combos to see PAR ratings, power draw etc. I used it to decide on toe 175 Iwasaki. Almost the same output as a 250w 20k bulb but saves me on electrical cost. Good luck with your choice.