R-26 will usually produce higher velocities than R-22 and also can usually handle up to 1-1.5 grains more than R-22 depending on cartridge and load. Cross reference the load and watch your chronograph as the pressure will sneak up on you with R-26 especially over about 85-90 degrees temperatures.

I have been in Alaska when the temperatures got this high or more but the water was still too cold for swimming. Did one lap across the Unalakleet and I think I could have sung falsetto afterwards, didn't try.