I am going for one of every front, and trying to acquire one of as many backs as I can along the way. Depending on the back, I will downgrade a cards grade to get a better back. For example, I had a common in an SGC 40 with a Piedmont back, but I "downgraded" to a PSA 2 with a Hindu back. Hindu is my favorite back, so I try to get as many of them as possible, but I would like to have as many different backs as possible. I'm shooting for 518, but that is based on my current financial situation. I am only at 101 or 102 right now, so who knows if that situation will have changed when I am approaching 518-520, or what the market will be at that time. Whatever....I'm having a blast.