I think MH's are overkill on any freshwater planted tank unless you have a minimum of a 24 inch depth. If this was saltwater though, you'd be set.
I have 2 400w mhs from my salt water tank..you will get about 2 maybe 3 feet of coverage depending on the reflector. Dont get me wrong it will be intense light, but it wont cover an area any more then that.
If I were you I would get some t5's and save the money on electricity. However free is free, and if you dont have the money for t5's then go with the 250's. Just make sure you keep an eye on your temps, and you better start dosing and cranking up that co2!