Only 3? Well I think I may have bought 3 in a day now and then, so don't feel bad. LOL
Been there...Done that. The difference between 3 and 4 is only one. Doesn't that make it sound better? I love Kooba and Gustto so I can't decide for you.
You picked all pretty large bags there except for the Baca. Which is medium in looks but holds an enormous amount. The smallest of the koobas would be the Lena. It's a Medium to large sized bag that is somewhat weighty.
My suggestion would be to look at these bags on Active Endeavors because they usually have pics with a model and you can get a general idea what size the bags are. Keep in mind that the models are 5' 10" and 95lbs...LOL