After quite a hectic schedule the past 18 months at my new ventures, I finally think i am good to return to my passion (Photography). However, need to revamp my photo gear. First start was the body and here is the new baby . . . Now planning a decent L series prime. What would be a good light weight prime, mostly for birding / mammals, which will compliment my existing glass collection of 70-300, 100 - 400 and the 150-500. Do let me have your thoughts and advices.