My two cents

I fly the very 'light' models you speak of ( disc loadings of around 3.5). I have extensively tried both two and three bladed hubs using the same type of hub construction ( wood polypropylene sandwich) and identical blades. It became very clear early on that three blades gave more lift and increased stability than the two blade hub.
Rpm on the two blade hub was noticeably higher but was more difficult to initially spin up.
I will in future only use three blade hubs as I found the easier build of a two blade hub is more trouible than its worth getting it to perform right.

These are just my own findings so hardly represent a conclusive result.

Sean