4k Video Editing, What Do You Suggest?

Hi guys. I just moved up from 1080p to editing 4k video and my setup is suffering. I can't playback the native files on quicktime without severe choppiness. Once they are imported into Premier Pro CC it is better but not great. I have a feeling it is the hard drive speed?

What do I need to do to bring my computer setup up to speed? Would a thunderbolt RAID drive fix this issue or is it the CPU?

I have an IMac 21.5" late 2012 3.1 Ghz Core i7 16GB RAM, NVIDIA geforce GT 650m 512mb, 1 TB Fusion drive, and several 2TB usb 3.0 My Book (Western Digital) drives.

Yea with higher than 1080p you will need a speedy DAS (Direct Attatch Storage), the fastest one you can get! Plus it doesn't hurt to gave a full Mac with it's speedy internals. Right now a Thunderbolt 2 DAS like the OWC Thunderbolt 2 External. Just be sure you use at least 7200 speed drives in your DAS.

Adobe Premiere accepts wmv, mpeg as native video, and you might need imedia converter for Mac from Pavtube to transcode those 4k videos beforehand.