Any experience we have had with sub 4inch drills is that in anything other than perfect conditions they are a pain in the a**e for blocking with sods,stones etcthink getting under 4 inch will mean going to 4 rows of tines to get the spaceings and trash flow
biggest probs with 4 rows is distance from front to back row for ground following on hills and would mean air seeder to get seed down the hoses