I had a set of Kirchner duals on a 2188 a few years back. It did much better in rows than the single 30.5's on that combine. I would expect the 9750 to be similar in that respect. I have a set of 20.8X42 duals on my present 9750. I haven't put it in rows and don't plan to. I only use it in rice. As heavy as that machine is, I can't imagine running it with anything other than duals or tracks. By your handle, I assume your combine will spend some time in a rice field. If so, I would recommend you find a set of 28lX26's for the rear. With duals on the front and skinney singles on the rear, your rear end will be the weakest link in a muddy field. The front end stays up pretty good, but the rear will get you stuck. With the 28's on the back, it's a much better balanced machine in the mud. I run the skinney rears most of the time (makes narrower tracks in the field),but won't hesitate to put the fat ones on if it gets wet. If you can find a 550 massey in a bone yard with the 28's on it, they will bolt to your 9750 with no changes (if your machinge is set up for 30" rows). You don't even have to change your spacing. The inside of your rears tires runs even with the inside of your front inside duals. I can't tell you which set of duals would be better for you machine. The Kirchners are well made, but so is the Deere set up. I'd lean toward which ever ones I could get into with the least amount of cash.