The SiSoft Sandra 2013 CPU Arithmetic benchmark shows the i5-4250U found in the MacBook Air outperforms both the AMD A4-5000 Kabini part and the previous generation Core i3-3227U Ivy Bridge low voltage option. Both the desktop i3-2105 and the desktop AMD Trinity APU outperform the i5-4250U however.
In the Single threaded CineBench 11.5 Render test, the i5-4250U actually manages to beat the highest end Trinity desktop APU, and comes close to the performance of the desktop Sandy Bridge part. In the multi-threaded test, the dual core 4250U cannot keep up with the quad core A10-5800K or the i3-2105.
As for x264 video encoding, the i5-4250U outperforms the cheaper AMD A4-5000 part, but falls short of the desktop AMD A10-5800K