agreed, why do you want to replace the t5. and a single 150w mh isnt going to do it with a tank of those dimensions, and what t5 lighting do you have now ?
HAHAHA you know what light I am going to recommend.
At least I can say this, it's your lost if you do not choose LED actinics. You can keep the T5 or switch to MH for main lighting application but still use LED as actinics. It's the only technology now to narrow down to the right wavelength so that the corals' fluorecense is fluorescent not some washed out fluorecent like the T5/PC actinics.
Note: LED actinics does not alter your corals' color but just show you more exact fluorecent color of the corals.