I recently bought a GR2, and the reasons for not going to a GR3 was mainly because it was huge. While it is touted as the maximum carry-on size, it will not be allowed on certain airlines if fully packed.
Based on the stated dimensions of the bag stated here, 22″H x 14″W x 9″D, I created a chart to show which airlines will possibly pose a problem if your bag is fully packed.
Yellow are dimensions that are below the stated allowable limit, but with the GR3 compression straps you can probably get by. Red ones are the dimensions that fall under the GR3‘s dimensions significantly.
If the following chart helped you in making your decision, be sure to purchase your GR3 through this link. This gives me a small kickback that will help support this blog at no extra cost to you.