Think I could possibly get by running SMAC (I don't like SMAX) with these specs? 1.4 Ghz / 4 gigs ram.

While the game card for SMAC recommends a 1.8 Ghz processor, I've been able to run it with a 1.6 Ghz Atom processor and it still ran smoothly.

The retail version only required a 133 Mhz processor and 16 MB of ram http://www.allgame.com/game.php?id=14546&tab=sysreqs

How come the game card recommends a 1.8GHz CPU for a game that is really happy with 1/10th of that? What exactly did GOG do with the game?

I'm sure the reasoning is that:
1) Not all processors are made equal. One processor of the same "speed" might perform worse than another one.
2) Windows consumes more resources than it did when the game came out.
3) Testing on uncommon hardware costs money. Many computers made towards the end of the XP era and any capable of running Vista or later exceed the minimum requirements.

Well, I guess if GOG just posts the minimum requirement for the heaviest OS (Windows 7) I suppose it makes sense.

Well here I am almost a year later. I purchased Alpha Centauri from GOG and it works perfectly on my dual core AMD 1.4 Ghz machine. I could not find a patch to cure my old CD version of the game to work on Win 8 but the GOG download works perfect! Thanks GOG!!!! You guys ROCK!!!!

Realizing that this topic is already answered, I'll just post that I have this running on a similar system (1.4 GHz dual core, 4G (now 8) RAM) in Wine in Funtoo Linux. The load on said system is positively negligible (almost as light as a roguelike). Given that this game is turn-based, even if you are on a vastly underpowered system, then it shouldn't make a huge difference.