Gear ratios for no brakes riding...

What mental would use a thin-as-shit 10-speed racing chain if they were relying on it to slow them down?

10-speed chains are still 3/32" wide, I can't see how their perceived "thinness" would contribute to them being weaker, it is pretty much impossible to "snap" a chain link plate.

I would generally advise using the 3/32" (derailer) size. It is lighter, more compatible with your existing chainwheels, and likely to run smoother if the chainline is less than perfect, due to beveled side plates. In my experience, 3/32" chain is no less durable or reliable than 1/8".

mdcc's post is the best analysis of brakeless riding I have ever read, he backs his claims up with evidence.