This is a timely post as I'm in the market for a lightweight full face as I start to progress my riding into more challenging features but am not near a level where I'd need a full on downhill lid. These helmets are also so light I might just wear them daily, despite the dumb looks I'm sure to get. More protection is almost always a good thing.
I've narrowed my options to the TLD Stage, 100% Trajecta, IXS Trigger and Leatt DBX 4.0. All of these are in the lightweight and breathable category but many are still downhill certified. The Leatt is a bit heavier than the others but looks like has a bit more of a downhill flavor, hence the weight tradeoff. I'm leaning Leatt since I think an extra half pound or so is a small price to pay for more protection. The Stage is very popular, I just got back from Bentonville and it was obviously the full face of choice there. But it has a weird pad design where it contacts the lower half of the ears and I found that quite uncomfortable and in my opinion when it comes to helmets fit is everything. The Fox Proframe seems to be the 2nd most popular but there are some pretty mixed reviews on it out there, with some saying the that helmet breaks too easily on impact. I partially attribute this to the fact that negative reviews are usually more prevalent online, and that these helmets are likely designed to break on impact and then be replaced, but there was still enough chatter about it for me to look elsewhere. The Proframe shell also appears to have a break right where the chinbar meets the rest of the helmet which makes me question if that's a possible structural weak point, but I'll admit the shell design may not match the structural design underneath on any helmet so it's hard to tell. Now I'm trying to find stores with generous return shipping options to try on the 3 I haven't found in stores yet.
I also immediately ruled out any lid with a removeable chin bar. This is purely a personal decision but is based on my thought that anything removeable can't possibly be as strong as a permanently affixed chinbar, and the fact that I witnessed a motorcycle accident by someone wearing one of those flip up chinbar helmets and the chinbar completely separated from the rest of the helmet immediately upon impact.