The only issue with the 6" on each side is that you obviously have less light on the ends of your tank. Not a big deal, really. You just need to place coral accordingly. I actually prefer having darker areas where I can place low light coral and sponges.
My advice, since you don't really have that much of a budget, is to keep what you have. I think you'll be happier with the HO T5's than you would be with a cheap led setup. Six 36" HO T5 is A LOT of light. Especially if you are running any ATI Blue+ bulbs. Those things are PAR monsters.