I'm sure this topic has been discussed at length before, but as always what I'm really after is justification for the decision that I've already made 
I currently have a 70-300 IS non-L. I enjoy it, but I'm never satisfied with the AF speed. I used to own a 100-400 which was waaay quicker to AF, but it was too big for me. With the 70-300, I struggle to track moving targets with all my bodies - 40D, 100D, 6D - the AF just hunts far too much. I had no trouble with my 40D when I used to use a 100-400, and I have no trouble now with 100D or 6D and my other lenses, so I'm 80% confident it's not my technique.
Another problem I find is that I'm either in the 80-180mm range, or at 300mm.
My solution: replace the 70-300 with combinaton of 70-200mm f/4 and 300mm f/4. This gives me the option of getting an extender at a future date which I wouldn't have with 70-300 L, and gives me f4 all the way to 300mm.
It's about £1900 for the pair brand new, probably could get both for £1500-1600 second hand. I would sell 70-300, also 40D and 10-22mm, probably about £700-800, so would need to foot another £800 which I can do.
Thoughts? Let the mocking begin! 
