If I was at home, this would be as simple as plugging everything into my software. As I'm not, a touch of help would be appreciated if anyone has the time.

The quilt top center will end up 58.75" x 80.5". I'd like to add two borders, one 3" and one 6", to make the quilt a hefty queen-sized. How much yardage would I need of each border fabric to make this magic happen?

(Also, do you think it might be better to go with 2" and 6" or will the 3" be better? I know it's hard to say not seeing the quilt, but it will be a Cosmic Twist Bargello with plenty of small pieces.)

it's in the eye of the beholder.....whichever looks best to you and gives good balance. It is difficult to visualize without seeing a picture and know what sizes would balance the block designs. Also the amount of fabric you need depends on whether you cut he length of the fabric to avoid seams or cross and will put seams in the batting. Initial reaction is if you do a 6" border cutting cross of the fabric you will need a minimum of 46" plus some. But don't take my calculations. You need to measure the exact and do the calculations from that.