If it ain't broke don't fix it. If your tank doing awesome don't change lighting. It's not that much in saving looking at the long haul. A rapid led fixture takes about 180 watts to run. You will be running them longer than your mh. A 250 mh runs about 250 to 275 watts. It's not that big of a difference. I switch from mh to led back to mh as certain corals do as well.
Running 60 3W emitters at 100% rated current would be 180W, but that would be one HELL of a powerful array for a 36" tank.
LED pros: You'll use FAR less power per lumen to illuminate your tank. something like half as much, in fact; MHs are hideously inefficient. You have more control over both the brightness and spectrum, versus MH/T5s. They run much, much cooler, which is of concern of your lights live in an enclosed hood, but less so in a pendant. They don't burn out or change spectrum over any realistic time scale, so you don't have to buy new bulbs every six months.
Cons: You have more control over brightness and spectrum. :lol: This can lead to people building arrays with four white emitters and seven hundred royal blue and UV emitters, to try to make the UV-sensitive colors of their corals show up like they did at the store. You don't HAVE to do it that way, though. They're also slightly more expensive initially, and theyre electrically more complex, which can mean they're more difficult to set up. There are spectrum questions with LEDs, but this can be solved with emitter selection and array layout. Lots of people also see LEDs with a bit of superstition, as I've heard of quite a few going back to MH (not just the ones in this thread,) after an experiment with LEDs, but simultaneously, I know of several AMAZING LED-only tanks, whose owners wouldn't give up their lights for anything.
It's a matter of taste. Also, if your current MH setup is working, it can be hard to justify the upgrade. As I said, they are legit expensive up-front, if you want them done properly.