Anyone use these lenses? Canon 100-400mm, 70-300mm, 28-300mm
 

Looking to get something with more reach than the 70-200mm lens. Does anyone have experience with any of these lenses on their C100 (or C300 / C500)? (Looking for any opinions, pros, cons, things to watch out for.)

http://www.bhphotovideo.com/c/product/732106-USA/Canon_4426B002_EF_70_300mm_f_4_5_6L_IS.html
http://www.bhphotovideo.com/c/product/319784-USA/Canon_9322A002AA_28_300mm_f_3_5_5_6L_IS_USM.html
http://www.bhphotovideo.com/c/product/162616-USA/Canon_2577A002AA_100_400mm_f_4_5_5_6L_IS_USM.html
(or newly announced) http://www.bhphotovideo.com/c/product/1092632-REG/canon_9524b002_ef_100_400mm_f_4_5_5_6l_is.html
Or should I just get a 1.4x or 2x extender?

http://www.bhphotovideo.com/c/product/732113-USA/Canon_4409B002_Extender_EF_1_4X_III.html
http://www.bhphotovideo.com/c/product/732111-USA/Canon_4410B002_Extender_EF_2X_III.html