A 706 would be pretty close 3020. The 706 was 70HP were as the 3020 was 65HP to the best of my knowledge. The 806 would be close to a 4020 since they are both 80 horse tractors. The Internationals had several advantages over the John Deeres. They were a heavier tractor and also would use less fuel. They also had and optional "Torque Amplifier" that would give you a slightly lower hydraulically shifted gear in each mechanical gear.
IH answered Deere's 4010 with the 806. Deere responded with the 4020. IH countered with the 856.
Deere's 3010 was matched by the 606. Deere came back with the 3020 The IH 706 was just a tad bigger than the 3020. Deere responded to the 706 with their 4000. It had the same engine as the 4020 and was more HP than the 706.
I always put the 3020 and the 4020 with the 706 and 806 although the red given all things equal ate the deeres for lunch while at the fuel tank getting refilled. The deeres never could pull the hills well between lower torque rises and the constant ballast changes between full tank of fuel and empty they were touchy as to when you could do what you might need to do. We had 706's pulling four and five bottom plows here and the 3020 at best was a slow four and most 4020's just pulled four.