good question, i'm going in July and planning to take 24-105, 50 1.4, 100-400, 400DO (rented), and 1.4X-II with 5D (or 40D) and soon-to-arrive 5DII. i'm going to do some testing, but won't be able to test the 400 DO until shortly before i leave. also taking a 580 flash with better beamer for daytime fill and night, and probably a 72mm 500D.
i've used the 100-400 a lot with 20D and 40D and the 400DO on one trip with the 40D
my limited experience in africa is that the 100-400 is really useful on a crop frame camera with quite a few images at 640 equiv - but lots of images at less than that. and there are a few times (mostly birds) where 640 isn't enough
additionally, f5.6 isn't fast enough in the morning and late afternoon (and the 100-400 isn't very happy at f5.6 either) - hence the argument for taking 5D and 5DII which both have lower high ISO noise than the 40D - using the 5D on the 100-400 and the II with the 400DO with or without the 1.4X.
will a 40D with 400DO have better IQ than 5DII with 400DO+1.4X (assuming adequate light)?
will the 400DO+1.4x 40D for 900mm eff be better than a cropped 5DII? - i think it will, but
will using the 5D & 100-400, 5DII & 400D)+1.4 should result in fewest lens changes? - dust is a problem even with ultrasonic cleaning
i hope your 70-300DO is a lot better than mine from 200 to 300 - and i hope mine is better when it gets back from Canon repair - so far it's been useless for wildlife, and not something i'd put on a 5DII even if Canon does make it better - i'd definitely recommend using the 70-300 on 450 (and using it at longer focal lengths only if you have to). And i'd definitely recommend a 1.4XII (i found it to be enough better than my original 1.4X to justify replacement) to use with the 400DO
curious why you're bothering to take the Sigma 18-125 when you have the 24-105. also expect that the 10-20 will get little use
i'll let you know what happens when i get back the end of July, in the mean time, i'd also like to hear from someone with direct experience