"Thunderbolt 2 introduces DisplayPort 1.2 support to the Airs, which when combined with the new Haswell GPUs will enable 4K output at 60Hz."
That's a typo too. MacBook Air with Thunderbolt 2 (2015) has Broadwell, not Haswell. That aside, the claim that the new CPU/GPU will enable 4k output at 60 Hz seems to be supported by Intel info, but contradicted by Apple info.
If you look at the Intel link above, under "Display and Audio Features Comparison", it says Haswell (4th generation) supports only 30 Hz, while Broadwell (5th generation) supports 60 Hz. But the Apple link says the Broadwell MacBook Air supports only 30 Hz - while the MacBook Pro Retina 13" supports 60 Hz, even though they both have Broadwell U-processors that should support it.
The new MacBook's Core M processor on the other hand is listed by Intel as being 60 Hz "capable" but with "additional cooling required". So I would bet that Apple's fanless design is not going to support that. But why the new MacBook Air wouldn't support 60 Hz is a mystery to me.
Some Sonys do support HDMI 2.0 already. To use an Ultra HD TV as a desktop computer monitor via HDMI, the TV needs to support HDMI 2.0 *and* full chroma sampling at 60 Hz:
http://www.anandtech.com/show/8191/nvidia-kepler-cards-get-hdmi-4k60hz-support-kind-of
...then you have to wait a few months from now to buy a DisplayPort 1.2 to HDMI 2.0 adapter:
http://www.avsforum.com/forum/35-ca...-1-2-hdmi-2-0-adapter-there-manufacturer.html
Unfortunately, I think your X850A doesn't support that - not sure.
This is all in theory though - at the moment we don't know which Macs (if any) would support 60 Hz Ultra HD through such an adapter.