iPhone 4K Video Choppy on Mac Pro (Early 2008)

Hello,

Just upgraded to the new iPhone 6s. Took a bunch of awesome 4K video, but my Mac Pro can't keep up.

Mac Pro (Early 2008)

Processor: 2 x 3.2 GHz Quad-Core Intel Xeon

Memory: 16 GB 800 MHz DDR2 FB-DIMM

Graphics: NVIDIA GeForce 8800 GT 512 MB

Display: 30" Apple Cinema Display

What can I do to help the videos run more smoothly. I don't need a 4K monitor... or do I??

Thanks!

Mike