I have always wanted the 1d x but am unsure the extra $3k is worth it for me. The pro's for me are better iso in low light and af point metering. Cons size and could that money get me a nice 35 mm prime and maybe a 1.4iii teleconverter and keep my macbook. Just stuck on the decision. Any suggestions?
Ok, I'll play along. You haven't given me a convincing reason to do that. So, you "always wanted" the 1Dx. Why is that? Because it looks cool/"pro"? Because there is something it can do that let's you make better pictures than your MarkIII? Because you shoot in conditions that require an even more rugged body?
Sorry, but the "better ISO" is about as reasonable as saying you don't want the 1dx because of its "lower megapixel count". It's irrelevant almost always. I've never found a reason to shoot at anything higher than 3200 - and that's extreme and on a MarkII. Up to 800 does the trick in 99% of the cases I would argue. I must admit that I still operate under the rule of thumb that if it worked on film and my DSLR does the same thing or better I'm set.
Same with AF point spot metering. If my camera had that I'd turn it off. And I use spot metering quite a bit actually. Just point at what you want to meter for, lock the reading and then focus as you normally would. It's really two separate things and what you focus on does not necessarily be the area you want to meter for.
Invest in glass or light, and enjoy your fabulous MarkIII/Macbook combo. With that camera and post processing ability there is absolutely NO excuse for making mediocre pictures.