FWIW, I wouldn't use anything but a Surefire light. I've had the same X200 for about 5 years, and it gets daily use. It's certainly not babied. I haven't been able to break it, and that's saying a lot. The other guys on my team use Surefires as well on their pistols, and our shotguns have dedicated SF fore end lights. My M4 wears a SF light as well. You can't go wrong with a SF weapon light.
Check with the folks at Wilson and see if the Dawson rail will fit. I'm sure it will but I know they'll be happy to discuss it with you. When I ordered my CQB/rail they were more than helpful, and they've always been great whenever I've called. The Dawson is rock-solid since it bolts to the gun, so it's a good option. Of course, it will need to be installed by a gunsmith, where the SF mount is a do it yourself deal.
Some of the guys in my company mounted lights on the POS issued M9s using SF mounts and they were happy with them. But like I said, the mission drives the gear train. Is this going a carry gun, or a nightstand gun? Police use? Are you comfortable with a permanent mounting solution or do you want to be able to remove the mount easily?