For years we ran Kuchar concaves and grates on our machines, but when we traded this year we were stuck with the CaseIH stuff. We did have 3 extra Kuchar grates laying around and we put those in, but otherwise we would go with the slotted grates. The machine came with three small wire concaves and we weren't happy with their performance, so we slapped a cover plate on a large wire concave* that we had for corn and put it in the first position. That made a big difference.
I've thought about using one keystock grate in really tough-threshing wheat, but never tried it. I would think three keystocks would be too aggressive. The slotted grates should work best.
*The only reason we used a large wire concave with the cover plate was convenience. We put the plate on in the shop while waiting for the dew to burn off, then just swapped concaves at the field. Then there's the added benefit of only having to change two concaves between corn and wheat.