All the reading that I have done has said that technically an SYE/DC drive shaft are not needed for a 4" lift, however, they are VERY HIGHLY RECOMMENDED. If they are not done you will need a very large TC drop to correct your drive line angles (and as stated above, that defeats the purpose of the lift). From most of what I've seen here the largest SL you should do without an SYE/DC drive shaft is 3". Most knowledgeable people here would recommend, if you require 4" of lift, to do a 3" SL and a 1" BL. A popular solution is the 4.25 combo lift from Zone (which actually has a 1.25" BL and a 1" MML).
Also, if you do get the SYE and DC drive shaft you will need adjustable control arms (I believe upper) as well to correct your pinion angle.