Xr31 are def. more aero than xr22. But remember, these are alloy rims. If you really want aero, you need deep section carbon rims. At least 35 mm in depth. Preferably 38-45 mm depth with your weight.
This is a popular conception, but I'm not sure that it lines up with the data (actually I'm certain it contradicts the data I'm just being tactful with my wording). For example, let's compare an Enve 3.4 and a Kinlin XC279, both with 23c Continental GP4000sII tires inflated to 100psi (A2 wind tunnel protocol inflation). If we take the yaw points of 0-12.5 degrees at each 2.5*, and weight each equally, then the front wheel difference totals 11 seconds over the course of a 40k TT at 30mph (wind tunnel protocol speed) in favor of the Enve 3.4 front. Since the rear wheel has only about half the aerodynamic impact of the front, the difference in a full set of wheels would favor the Enve 3.4 by 16.5 seconds over the course of the 40k TT at 30mph.
It is now much more broadly accepted that low yaw angles predominate in actual real world yaw conditions, with yaw angles of 10* or less occurring over 75% of the time, and angles of less than 5* happening about 50% of the time. So if you simplify and only look at what happens at 10* or less, the Enve 3.4 set is slightly less than 12* faster over the course of our 40k TT.
To use a Velocity A23 as a stand-in for the 22mm Kinlin (we have data on the A23 but not the Kinlin 22), the greater drag exhibited by the A23 at low angles of yaw means that the difference between the 22mm deep Kinlin 22 and the 28mm deep XC279 is more than the difference between the Kinlin XC279 and a Zipp Firecrest 404.
So of course it depends what one defines as "aero," but if you use currently accepted yaw angle distributions, as measured by Bontrager and Flo (even in windy, wide open locations like Kona, where they both tested), then the difference between a very shallow rim like an A23 and a deeper and well-shaped alloy rim is greater than the difference between the deeper and well-shaped alloy rim and a deep, aerodynamically oriented wheel.