To me, the question depends on what your customers use fat quarters for - I've made a lot of things with bundles of five (totes, place mats, baby quilts), have also sprung for larger bundles if I know what I'm using them to make.
For me the larger the bundle, the more I'm relying on you to coordinate the fabrics on my behalf (some days I really need the help!). But sometimes I'm intimidated by such a large grouping so can talk myself out of it. Some of the fabrics you've previewed for us here often have ten or more combinations and I usually want them all, but I can't mentally visualize all of them in a single project.
They say the reason telephone numbers are seven digits is because that's all our little brains can comfortably manage. And maybe theme bundles are another idea - Lucky 7, Wicked 6, Lost Sox 9 (none of them coordinated but somehow cool together), Baker's Dozen, Advent 24...
I think offering your own combinations is a great idea, and smaller bundles are more likely to sell. I also like the idea of custom bundles, I'd suggest these could be offered if buying ten or more since your costs are in the cutting.
My apologies if all this makes your head spin, my hubby would be rolling his eyes at my philosophizin', so ignore whatever doesn't grab your interest, and thanks for letting me ponder out loud.