There was quite a lot about the patches and relative synch for mac and PC, I don't recall the exact thread, but basically the Mac and PC versions are not in synch, have not ever been in synch, and are not (yet) intended to BE in synch. I even emailed Firaxis and tried to get some specifics, but basically the answer is "maybe someday". The patch numbers actually appear to be closer than they were before, so maybe the gap is closing. Right now, I believe your only option is to run the PC version in Boot Camp or try out Parallels or some other Virtual Machine. Through my searches it has appeared to me that Boot Camp is more likely to succeed.
I can't say I know this for a fact, but a couple of strings lead me to believe that the MAC patch will always lag the PC patch, due to the vendor relationships with FIRAXIS.
I will tell you, however, that it IS THEORETICALLY possible to somewhat control the version you are on... at least in the "don't patch me yet" department... in Steam you can choose NOT to autopatch. This would ONLY work when the patch was a single step ahead, since you still cannot control which patch you are on.
Thus, theoretically, you can control when you "patch up", so if the PC version is a patch ahead, the PC player would choose NOT to auto patch, and would only patch when the Mac version was caught up... of course that would require an overlap window, which will be beyond your control. Of course, I've never yet heard of anyone successfully doing this.
It does not appear that allowing PC and MAC players to play simultaneously in MP is a present priority.
-p
