100-400IS + 400 f 5.6

I currently own the 100-400mm IS lens and love it. No lens is perfect though and I feel it is a little slow focusing at 400mm. This is particularly apparent when photographing birds. I am considering adding the 400mm f 5.6 for this type of photography. I want to make it clear that I will be keeping the 100-400IS not replacing it. Does this make any sense?

the 100-400L is also a f5.6 @ 400mm so by adding the 400 f5.6 to your collection won't make much difference. the speed will not be much faster although the prime will have slightly better IQ. so a waste of money IMO.

Makes perfect sense to me, I own both. The 100-400L for traveling, flowers, insects, zoos. The 400L is my bird lens, the focus speed is significantly faster.

tthe 400 5.6 is a beautiful lens. absolute shamp for birding, and very light. i will never be letting go of it, not even if/when i get a 500 F4. it cant be beat for its sharpness/speed/weight for flying birds.