Txurce
Deity
I quite like the new Darius, certainly much more than the older one.
The fun I got from Darius was trying to maximise Golden Ages - the entire game effectively became making my people as happy as possible, while going for any policy that would benefit Golden Ages, in order to get the upper hand in culture. The UU is especially cool in this regard, since using the Immortal against Barbs is more of a tool to get more Golden Ages than to have a promoted army.
Siam, in my eyes, has always been the strongest Civ - the one contender being vanilla Korea. He does have a tendency to runaway, and it's primarily due to the extra food he gets.
Siam will do better now because the extra gold funnels directly into his UA. From that pov, he just received a huge boost as an AI, and needs nerfing. However, Persia outperformed him in my game. I agree with albie that Persia is almost uniquely hands-on, in that you are constantly pulling its levers to reach and stay in a GA.
With regard to evaluating these civs, I wonder if Prince is the level on which to do it? In other words, should Siam be measured on Prince, or on a higher level where it's getting (warped by definition) bonuses? Also, is it running away with games (not my experience) or merely establishing itself as the most consistent AI? My sense is that it's the latter.
Edit: Also keep in mind that the human player wouldn't get the same advantages as the V132 AI. A nerf would make Siam less appealing to the human player (who should take priority).