Rough calculation (CMIIW):
Amex cost is $294 (net gain of $6) + (300 MR (@ $.012) = $3.60) total net gain of $9.60
Ink cost is $309 (net loss of $9) + (1500 UR (@ $.015) = $22.50) total net gain of $13.50
You are missing the "AMEX Offer" out of your equation (though as I said before, I think it would be better to Maximize the AMEX Offer, as it is only for a single purchase). Also, with Simply Cash card one gets 5% back on office supplies, so combined with the Amex Offer of 5% back on a single purchase as Staples, that sounds quite sweet to me. I would do 5x$300 VGC+ 2x$200 VGC as they limit the total purchase to $2,000, and in my experience that includes the activation fee.