Problem is there are a lot of variables when configuring your printer that affect the final margins -- and unless somebody is familiar with the exact habits of the 7880 or 9880, they probably won't know for certain. I don't know what the specific margin settings on the 7880 are, but can speak to the x900 printers if they're similar. On the x900's, you can choose either 15mm or 3mm margins in various combinations. Next, the paper size created will dictate where that margin is measured from. So the amount of paper "wasted"is equivalent to the margin chosen plus however much of the paper size isn't used. Next, the cutting method and and roll paper setup for borderless or banner also affects final margin placement. So if I were to print an a 21x28 print centered on a 24x32 paper size on a 24"roll, I would have approximately 2"extra top and bottom PLUS whichever margin size I chose -- 3mm or 15mm -- and then 1.5 inches extra on each side.