joykafka
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 p.1 #6 · 100-400 plus 200 2.8 + 85 1.8 | |
When you add 1.4x TC to 200/2.8, you get 280/4. You still gain about one stop than 100-400.
When you add 2x TC to 200/2.8, you get 400/5.6, just equivalent to the aperture of 100-400 @ 400mm.
However, if the focal length from 300mm to 400mm is frequently used, I see no significant gains in aperture, while I would notice a drop in image quality and in AF speed. Then, I would guess your best solution is to use 5D mkII at ISO 6400, 12500, or 25600. If you are using 40D/50D, probably 70-200/2.8 could be quite sufficient in terms of telephoto?
Just my 2cp. I seldom shoot sports and wildlife and I had no experience with 100-400. But, 100-400 is the first priority in my list if I am going to shoot more pictures of this sort. Probably, you can lend me your 100-400 to make sure if it is a suitable tool. 
A few lenses that I feel meaningful to add to 100-400 are:
Canon's or Sigma's 300/2.8 or Canon's 400/4.
In place of 100-400, Sigma's 120-300/2.8 (plus 1.4xTC), or
considering that you seem to prefer primes: 135/2, 300/4, 1.4xTC, 2xTC.
If you do anyway need large aperture specifically at 200mm and 85mm, I would think a 135/2 plus a 1.4xTC simpler.
Kafka
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) or now I am thinking for them dark days maybe using a 200 2.8 II for football and some baseball. But when I am behind the plate in baseball I could use a 85.