I have both the GST and the jumbo and I think that you'll end up liking the GST...at first, it took me awhile to get used to the boxiness too but once I switched to the GST and the amount of stuff that I can put into, my jumbo hasn't gotten as much time out of my closet. Also, I've noticed that the newer washed caviar is a little softer and tends to mold to your body faster, so maybe if you give it a little more time, it'll be more comfortable.
In the end, I think it also depends on how much stuff you like to carry with you. I fill up my GST so when I carry my jumbo, I have to not carry half the stuff that I normally carry around with my GST. That's why my jumbo has become more of my going out purse than my everyday bag that I take to work and run errands with.