This might be kind of late but I'll tell you what we figured out from the class I took. I'm pretty sure the class was the "Stacked Posie." The more contrast between the background and the pattern the better the kaleidoscope stands out. The size of the repeat doesn't matter so much as the variety in each repeat. The less variety in each repeat the more blocks you'll get that look the same or similar. I would say you want the repeat to be at least 10 inches to get the most out of your fabric.
I highly recommend shopping.