Bill

You had mentioned that you thought your copy of the 100-400mm is soft even without the TC. If your comparison is against a 70-200mm F2.8L II then I think indeed it would feel soft as the 70-200mm is a much better lens IMO. As mentioned your 7D and 5D II wouldn't focus with the teleconverter anyway. But that really shouldn't matter in your decision to get foCal because it is your camera that will not focus at F/8 no matter what type of system you use to set your AF adjustment. Another thing is shooting with a TC on the 100-400mm may not matter to you any way, because it may never produce the quality you are looking for. I suggest you test your 100-400mm to see if it is really soft, or it is another problem. Set it up on a tripod and take test shots using live view and focus on 10x. If you can't get what you believe is acceptable sharp IQ doing this, doing AF adjustments will not help.

Good Luck
Rick