Wait... say we have 10 Saturns, at 200GH/s each, and 1 Jupiter, at 400GH/s each, totaling 2400GH/s. A total of 923 shares (78*10+143) have been issued to buy those. That equates to almost exactly 2.6GH/s per share. Doesn't that mean every shareholder gets 2.6GH/s, regardless of which machine they "bought", and the only meaning of who bought what first is in what order they get their shares?
I think that's the most straightforward way, and anything else could negate the point of a mining company since all shares would not be equal. I might be biased though, since I'm in for Saturn shares.