My opinion is that the perfect amount of light is the amount that you want to keep up with. My first planted tank was a 30 gallon with 60 Watts of NO flourescents. And by and large it went very well. Not able to keep everything, but stuff grew.
When I got back into PTs about a year and a half ago, I got a 45 gallon tank that is 25 x 18 x 24. Different shape, but basically the same amount of surface area as the 30. I put 130 Watts of PCs over it. I regret that now. It worked fine while I was finishing up school and had the time for it. But I can't keep up with it now. It requires too much testing, too much fertilizing, too many water changes, etc, etc, etc.
Right now, I am in the process of getting together a 120. This is the size tank I've wanted to get for years now. A year ago, I was planning to use 2 x 150 Watt metal halides on it. Then I thought, that's too much. Then I figured 4 x 65 Watt PCs. Nope, changed my mind again. What I've finally settled on (as in I've already bought it) is a 4 x 54 Watt T5 HO fixture. But it has 2 switches on it, so I can halve the light. My plan (subject to further experimentation) is to run each set of 2 lights for 8 hours a day. They'll overlap in the middle giving 3 hours of 108 Watts, 5 hours of 216, and 3 more of 108. Why? Because I don't want to put up with the hassles of maintaining a high light tank.
You could definitely run a 120 with 2 x 250 MHs. Or 2 x 150. Or 4 x 65 PCs. Or 4 x 54 Watt T5s. Or 6 NO flourescents. Or a lot of other combinations I'm sure. Question is how much maintenance you want to do.