Largest-Scale Ligation (Help)

[JnP]

Hi, do people know what the largest ligation could be (both
theoretically and practically)?  As far as I know, those that 
have been used for library constructions go up to a complexity 
limit of 10^7.  Now I am wondering whether there is actually a 
practical limit to the number of different sequences one can 
handle in a single ligation reaction.  Also, I would like to 
know the linear range (of insert/vector concentration) within 
which one could get to increase the complexity.  (I have a 
pool of degeneracy of 10^9 that I wish to handle, but I don't 
think I will get to do 100 ligations or such.) 

All opinions, experience, and advice are highly appreciated. 

Many thanks!

-Jing Huang