To answer your question, yes the 6" is the go to one for combines and large tractors.  

I use the blaster and I think it works well.  You do have to be extremely careful though that the 4 metal wands that spin around never hit anything, they break off way too easy and not cheap to replace.  Set the depth correctly and always go slow straight in and out.  When I inquired about why they break so easily, they said it breaks instead of damaging the filter.  If that is their logic, they should make the part that breaks cost less than 50-60 dollars to replace.