Good point about the heat.
HID bulbs have a higher surface temp. Halogens produce more radiant heat.
I've ran mine for 15-20 minutes in the garage and the lens was hotter with the oem bulb. Keep in mind, the factory bulb is 55w and the HID's I put in are 35w, so it makes sense that they would be cooler. HID is more efficient at converting energy into light.
I love LED lighting too....got those on a few of my toys too. The one thing I'll add is that I haven't had real good success swapping LED bulbs into reflectors originally designed for Halogen bulbs. The focal point of the light is very different. LED's require a different reflector. Better off to buy those as a cube light, Rigid, etc. HID's work fine in a halogen reflector because the focal point of the light is the same or nearly the same position. LED's also excel at a spot beam if that's what you are going for (but again, buy the whole light, not just the bulb). HID's in a halogen reflector are very much a flood light, which is what I wanted.
The only downside to my upgrade that I've found is that it takes a couple seconds for HID bulbs to heat up from ambient temp. If you're only going to flash them on occasionally, they're probably not the best solution. I tend to run mine for more prolonged periods of time.
On my hunting four wheeler, I run HIDs in the factory headlight housing and LED spot cubes on the rack. They compliment each other nicely.