It'll be fine for fish only tank. However, the light will be a little bit yellowish in color. Halogens also produces more heat so you wouldn't want it too close to the tank.
I ordered some low voltage 12V Ushio Whitestar 50W 6,500K MR-16 halogen lamps for my track lighting. I'm also getting a few portable fixtures so that I can experiment shining the Ushio halogen spotlight directly at some Acroporas to see if they'll change colors.
The bulbs I ordered were these
http://www.ushio.com/files/WhitestarSpecSheet0302.pdf