I just picked up my 13" rmbp yesterday and I went ahead and installed fcpx. I then went ahead and edited some 4k video from my camcorder. I was blown away at how cool the 13" rmbp stayed while processing the 4k content! It was mildly warm, but thats it. Also, the new 13" rmbp can transcode/render 4k with ease! I was able to completely transcode a 3 minute 4k movie in just a couple minutes. The size of the final file was over 9gigs! This thing is a beast!