G'day
I have sold my Ibex in the last week or so and will be replacing it with a Extrawheel but when I had the Ibex I did use the bag.
I found it okay, but it has as has been commented on less capacity than claimed. I also found it not easy to pack. I can pack my 90 L Macpac backpack better than I can the BoB sack and again I can do better with panniers.
I would also distribute my load with some on the front. I believe the ratio is something like 40:60. I am sure someone will have more accurate figures.
Regards
Andrew