First of all, how much cash do you have? If you use tripod there's no need for IS. Because when you turn IS on tripod it thinks you handheld it and shaking a lot it will try to correct and perhaps make your photo worse!





Less cash


Canon EF 300/4,0 L IS USM
Canon EF 400/5,6 L USM



More cash


Canon EF 400/2,8 L IS USM, with extender this gives you like 5,6 should give you like 1/1000 or more in shutter speed and you could use higher ISO 800+


Use 1.4 instead for 2, it gives better images quality. Should be able to get nice shots! Probably your dream shots


But this setup probably gonna break your wallet if you don't have much cash to spare