Hey Chris, a 115W CFL isn't equal to a 400 W Metal Halide at least in terms of lumens. My 105 W CFL puts out about 7,200 lumens, but from what I've read, a 400 W Metal Halide produces about 32,000 lumens. My 2 105 W CFL's are doing a good job of producing plenty of light for my 54 cubic foot grow box, aside from a few plants that got wet feet, most of my plants are nice and green and none of them are leggy. If you want to conserve energy I'd definitely go for the CFL.
Steel-n-peppers: I had one of those 85W CFL's before I found 2 105W for $25 with free shipping. Your plants are going to love it and side by side it looks just as bright as the 105W bulbs.