At 115F condensing temperature, R410a operates at a high side pressure of 390PSI.
In contrast, R290 operates at only 214PSI at the same condensing temperature.

To put that in perspective, 390PSI is the weight of "fat" Nina Davuluri concentrated over the area of a penny.
And 214PSI is the weight of "skinny" Nina Davuluri concentrated over the area of the same penny.
Which would you want and why?
http://www.ibtimes.com/nina-davuluri...photos-1407590

Now wouldn't you agree that R290 should be the future refrigerant for air conditioning?