I have both of those helmets - The Castle X 950 and the Mod 3. They are both great helmets.
The Ski Doo Modular series of helmets have a reputation for being a great fog free helmet without the need to run a heated visor. I ran them for years because I didn't want to deal with heated visor cable (fuses, bad connections, shorts, tangles, etc). The downside of these helmets is also what makes them great; the breath box. The rubber breath box works so well because it is tightly strapped to your face and covers your mouth and nose. I never really had a problem with it; however, I know some riders that didn't like having it stuck to their face all day. Additionally, the breath box collects a lot of moisture. BRP sells packs of cotton pads to line the breath box to combat the issue and they work well, but it does represent and additional cost over the course of a year. Lastly, if you are interested in running a Bluetooth comm unit, you are going to have a hard time doing it with the breath box covering your mouth.
I switched to a 950 last year solely for the ability to run a communicator. Running a cable to a heated shield did not present the issues I thought it would. Initially I would forget to unplug the cable when I'd stop to refuel and end up yanking it out of the visor. The cable will come unplugged every once in a while, especially if I'm really active in how I'm riding that day. After a few rides, dealing with the cable really becomes second nature and I don't seem to have any issues with it now. You'll figure out the best way to route the cable down your jacket and over your bars and those issues will go away. I've also never had an issue with fuses. I run an RCA adapter to the 12v on the dash.
The 950 has been a great helmet, I find myself using it more than the Mod helmet based solely on the ability to run the bluetooth comms. I also have come to appreciate not having the BRP breath box strapped to my grill all day. I don't think you are going to go wrong with either. One last thought, if you buy the Mod 3 and want to run a comm. unit, or get sick of the breath box, you can always get a heated visor for that helmet and ditch the mask. With the 950, it will fog without the heated visor over the course of a day. Both helmets are comfortable and I never had a problem with leaks. I do believe the Mod 2 has and extra vent that the Mod 3 does not. The 950 has 2 vents that work well.
Scorpion makes the 950 for Castle X. It's the EXO AT950, shop them both, you may be able to find a deal.
Either way you go, try them both on, a properly fitted helmet is going to save your life. If its too loose or tight - you're going to have an F'd up day.
All of this is just one man's opinion - except for the part about properly fitting your helmet!
