To give some comparison info. My yanmar’s range 1 1st gear is rated at 0.6 mph. This would be my gear/range selection choice for untilled ground compared to the FE35’s 1.2 mph
If you ground has been tilled previously (previous growing season) I think you will have very good results with your tractor and tiller combo.
If you are tilling ground that has not been tilled in several years (2+) you will be frustrated with 1st pass results. Be patient, make multiple passes if possible at 90 degrees to the last pass. Allow some time for the ground to dry if damp between passes. When you go back to same directional passes, try to till 180 degrees from 1st pass.
If a heavy clay soil, have a soil sample test performed (our local extension office does this at minimum cost) and add products as recommended. Gypsum is good in clays to loosen the clay. Fertilizer companies will fo soil test typically and usually free, but expect to sell you product. (Reasonable expectation in my opinion).
If you can not get acceptable results with this tiller, you probably want to consider a counter rotating tiller (pricy however).