John, I don't have detailed enough memory but I have heard where that sweet spot was. Actually, on the large frame 7000 series tractors which I'm most familiar with, there would be two sweet spots as they range shift. I had in mind the range shift is less than 10mph (some say they can feel this shift, but the tractors I've driven under load didn't seem to show it, I must have been in the wrong situation) and the sweet spot was in primary tillage range. My memory isn't good enough to allow me to post hard numbers. However, I've never heard any information to say the tractor was better efficient at that level.

One of the concerns I have with this particular discussion is that no facts have been presented. The posts here seem to suggest a huge gap in fuel usage, but I don't see any comparisons on a gallons per acre basis. Nebraska tests show the 8430 powershift to be somewhat more efficient (less than 5% difference) than the 8430 IVT. However, those are constant load tests that don't reflect the strength of the vari-speed tranny. For interest sake, the 8430 IVT has as good efficiency or better as the previous 8520 PS of the same power. All three tractors are listed on the Nebraska test site.

Deere has provided dealers with a fairly lengthy discussion of this very issue. Essentially, it suggests what is being said here. Constant, heavy draft loads will be more efficient with the powershift. The key point is the word "constant". I don't have a lot of stick time with this transmission as my job now keeps me to a desk, but past experience tells me that few operations will keep a tractor at max power for extended lengths of time. They might have a discussion available publicly, but I haven't looked for it.

One example I'll discuss is pulling a field cultivator. For my first field experience, I had the opportunity to run a 7810 IVT pulling a 30' 980 cultivator. If I wanted, I could keep the tractor struggling to maintain the speed I set, but when I lifted the cultivator for turns, the engine idled right down, instead of the usual revving up. That made the smoothest, easiest turning I've experienced. As the field I was in was fairly narrow, and I was running crosswise, I was turning a good portion of the time. Second pass, the tractor didn't work nearly as hard and tended to idle back fairly often. Net result, I think while in that field, the tractor was maxed out roughly 50% of the time. That doesn't include transportation or other times when it was coasting.

I guess that I would love to hear from people who measured both the acres and the fuel put into the tractor over a variety of conditions before I would get too excited about the fuel differences between the two transmissions.