I've always found 3-5 for strength, and 6-10 for mass everytime I google rep ranges and search the other BB sites.
I did do 5x5 and did gain strength, but I got more size by doing a 6x3, then 6,6,7 then 6,6,8 etc, til I get 8x3, then up the weight.
I do like to switch it up after a good break (right now I've been on break for 3 mos, LOL), But usually after 8-10 weeks or a plateau......