Resources.load vs LoadLevelAdditive which is faster

I am developing a game for iOS and am using Unity 3.5 (free) with iPhone basic. I am currently experiencing almost 3 minute loading times for my main scene. First off I know that my main scene is somewhat large and heavy (I have 9 terrains converted to mobile use with the t4m tool). My plan is to start with a nearly empty scene and then start loading in assets from there.

My question is should I be using Resources.load() to accomplish this or some other mechanism like LoadLevelAdditive?

resources.load is better, loadleveladditive has an overhead.
loadleveladditiveasync would be even better but that requires iOS Pro