Tegra 4 vs Tegra 3?? what's happening?

i Received my Nvidia Shield, very good device, but as a developper i compared the framerate of my Android program which run in OpenGL on my SHIELD and on my OUYA running with a Tegra 3, and the result is strange.
OUYA run a bit faster and in FullHD, while Shield is 720P??

Any reason?