I use a 7 foot rake behind my JD 650,,, about the same size tractor.
If I fill the rake with a L O T of gravel,, the 650 slows,,, but, so far, the 7 foot has been perfect.
You can easily remove a few tines, if your tractor is underpowered,,,
but, it tough to add them!! I am glad I got 7 foot.
Whatever you do,,, get the gauge wheels,,,