Zackod,
I have been wearing an Arai Signet-Q for a number of years (size large). I had my local dealer order this Arai for me to try on. The Signet-Q happened to fit like a glove. I bought it when I tried it on.
Later my wife tried it; it fit her, too. We knew we had found our head shape and size in the Arai line up.
Just before our ill-fated trip to the Grand Canyon I bought my wife a Shoei GT-Air (size large). Our heads are the same size and shape (how'd that happen - IDK). I have worn both helmets at highway speeds and I am really impressed with the Shoei. I like my Arai a lot, but I think the Shoei is better in many ways.
[As you have noted, the Signet-X is the newer Signet in Arai's lineup. If you look at webbikeword.com's comparisons of helmet shapes (
http://www.webbikeworld.com/motorcycle-helmets/motorcycle-helmet-shapes.htm) they indicate that the Signet-X is a narrower fit than the Signet-Q and Shoei GT-Air. The Signet-Q and GT-Air are relatively the same shape, but see my comments, below.]
Here are my impressions of the two helmets we have (Arai Signet-Q and Shoei GT-Air, both in size large).
The Shoei is more aerodynamic; it seems to react less to turbulence than the Arai (slightly less; not a lot, but enough to appreciate there is a difference).
The Shoei large is a smaller helmet than the Arai large. As a matter of fact, the Shoei is really pretty hard to get on. Our Shoei is not broken-in yet, so I would think the difference in size will lessen. But the Shoei will still seem like a smaller helmet than the comparable Arai. The same comment is made in Webbikeworld.com's review of the GT-Air.
The Arai has cheek pads that can be easily altered. I removed one 5mm layer from each cheek pad on my Signet-Q. I will soon order new cheek pads for the Arai to return it to its original cheek pad fit (more on this below). The Shoei (size large) comes standard with 35mm cheek pads. If you want to "adjust" the cheek pad fit you order either thicker or thinner cheek pads; the cheek pads can't be adjusted like the Arai's.
Once you have the helmets on, the Shoei seems slightly smaller than the Arai (as above). Both are quiet helmets; the Shoei is quieter than the Arai. I will replace my altered cheek pads with new ones to see if the Arai is just as quiet when the cheek pads have not been altered.
The Shoei GT-Air's internal sun visor is great! The Arai Pro-Tour sun visor I have on my Signet-Q (an external sun visor) is very good, but, every once in a while when it is up it does catch a bit of air. And it really only has two positions, up or down. At speed it won't stay half-way-down reliably.
Both helmets work exceptionally well with our Sena SNH10R headsets. Our microphones are mounted to our chin guards and there is very, very little wind noise. Excellent!
I don't have an opinion about the helmets' ventilation systems. I ride behind a fairing so I'm sure ventilation is diminished to a degree on both helmets. I will say this, on cool/damp days without the pinlock visor in place the Shoei fogs up quickly when you're not moving (i.e., sitting at a stop light).
The Shoei visor does not seem to seal with "authority" like the Arai visor does. Shoei includes a small bottle of silicon something-or-other that is supposed to improve the seal - we haven't put it on, yet.
I looked online at the Signet-X for my wife. But I decided that the shape was narrower than the Signet-Q (see webbikeworld.com's comparison of helmet shapes). I went with the Shoei and I am really glad I did. My wife really likes the helmet. For a touring rider I think it really works well.
It would appear that you liked the fit of the Shoei GT-Air. If that is true, and if you did not experience "hot spots" on your head because of the fit/shape of the liner, then a similar-sized and shaped helmet ought to work well for you. Webbikeworld.com refers to the shape as a "slight narrow."
Hope this helps!
Bill
