How much can Unity3 handle? Vs unity4?

How big of a medium detail scene can unity3 handle? Is unity 4 more capable, as in uses more available RAM and such? I’m modeling the main free roam scene for a game, and its a city. Also, at what point should infinite terrain loading be considered? The map I currently have takes up 3.2GB as an FBX including textures and everything, and it is not complete. Thanks.

:::also, I know this depends greatly on other factors, like scripting and such. Most of the game will not be complex. Just looking for ballpark answers here.

There’s currently no difference between Unity 3 and Unity 4 in this regard; they are both 32-bit applications.