I'm going by the 16m measurement of the OT Y-WIng, which, for all intents and purposes, is the same ship just with its "skin" on it. There's been no indication that it's a different length as far as I know, as everything appears the same, just with the armor plating. The only difference structurally being the cockpit differences of course.
Definitely not in the 40" range though, no... That's huge, and YW's aren't actually massive like that in either the toon or the movie.
I'm not being real secretive about it though, honestly. I was just told a length by a friend with it, and his length may or may not be 100% spot-on correct. That's the only reason I'm remaining a little aloof about it. It may or may not be totally accurate. I'm assuming it was measured from guntip to the end of one of the nacels, and that it is accurate, but I'm not positive since I can't see it in person to be sure myself, haha. I'm particular like that.
I don't know why there'd be a discrepency in length of the two ships though... Nothing implies between the two that the CW3D YW is larger than the OT YW. If anything, it's implied they're the same ship, simply modified, and the OT YW is not some massive piece of machinery by any stretch. SW fighters are actually quite small compared to real-world modern day fighter jets.
I'm trying to put some positive vibes to this though. I think there's good things coming with it.

EDIT:
I see what you're saying about the two lengths on SW.com... I'm gonna call bunk on that though, as if you read the whole article the guy who designed it even acknowledges that he designed the Y-Wing for CW3D over top the actual model from the original trilogy... I'm not positive why SW.com is implying there's such a large size discrepency between the OT and CW3D ships, as that's a fairly significant difference when the ship's intended by the designer himself to be just stripped down. The only difference I could sort of imagine that could change the ship length like that, would be possibly truncating the nacels to remove "bulk". Regardless though this is something I'm willing to give a little creative leeway to, as EU is never consistant as we see here.
The only thing I'm disappointed in is the rear turret's design/placement, as compared to the CW3D model... Something I think I'm willing to overlook but which is a little distracting. I'm not buying the 7 meters worth of "length" being chopped off it though. That's, I'm wagering, some asshat trying to explain why we have this Y-Wing all armored up, along with the Y-Wing from the Cross-sections all armored up, and trying to say, "See both existed!", which falls into the usual trap of EU conflicting with EU, and nerds trying to make all this **** fit together, instead of just forgetting about one of the two conflicting things. Kinda like the different Spacetrooper designs and whatnot.
I was wondering who was going to try cramming the two Y-Wing designs together, and how they'd go with it.