That is some good info on the HIDs. When I said I changed all the bulbs on the Cobra, I really mean there are no regular bulbs left on the car...
Changing the scope to headlights low beam only - HID is king as far as brightness and ease of install. The light output is by far the main benefit, but when comparing to LED you can't really ignore the fact you don't have to do any bulb heat management either. It will be a while - but at some point I do want to retrofit my headlights with some new projectors and do the conversion to HID at that time as well.
It could be argued too - that is you retrofit a projector that is designed to handle the LED light beam - it should work as well assuming you can find some real 35W LEDs bulbs that will fit... To the point of everyone prior, I'm unaware of any such projector/LEDs for the W220.
Turns out you do need to do some heat management, because there is heat at the bottom end of the LED. They do run way cooler than incandescents, but they do still generate some heat, and LED's, being silicon-based semiconductors, are susceptible to thermal runaway (FET's are not, but both diodes and bipolar transistors are). That's why they have those heatsinks, and sometimes fans, on 'em.
You are certainly correct in that an LED in a projector or traditional reflector that's designed for that type of "bulb" will be very bright, indeed. We see this already on the newer USA Acuras (Hondas everywhere else in the world); their headlights are actually LED strips which are every bit the equal of HID's in output. Them things are BRIGHT. Currently there is work to do projector LED's, and when those do get perfected, they're going to be a fine choice. I'm looking forward to it! See, eventually, our HID projectors will burn out, like what happened with my S600, necessitating replacement. Should take about 10-15 years, depending on use. By then, really good projector LED's should be available at a reasonable price, sort of like what's happened with household LED light bulbs.
Your Cobra, by the way, is like my '90's-era Honda Civic. There is no computer to play nanny regarding the current usage, so the retrofit was conceptually easier. The only "complication" was that Civics use an H4/9003 bulb, which means a single dual-filament bulb in the housing. Hit the high beams, and the power to the "low beam" circuit goes off. Not so good when you're dealing with bi-xenon projectors, as you want that HID bulb to stay on continuously when you hit the high-beams; all you want to do is lower or raise the high-beam solenoid, as appropriate. Calls for a diode in the circuit, basically, and that solved the problem.