I would also consider a R-42, granted you won't break any speed records, you will keep the machine full. Whether you run an R-52 at 4-5 mph or an R-42 at 3-4 mph, the machine is full. We were considered putting an 8 row head and 20' platform on a R-42 because it had more capacity than our old White 8900 (we ran 2.0 mph in 200+ bu corn) on the 8 row head. We would have had to put heavier final drives on it to carry the 8 row head, and possiably an extra lift cylinder, but it should run a 6 row w_o any problems. If you have the handling capacity at the bin site, then the the 52 might work better since you can turn the truck around faster. If not, the 42 might be a better option since you will be running slower to give that truck more time. We ended up with a White 2600 (r-62) because it had (at the time) most of the updates, less hours and was field ready w_heads. The 42 hadn't come in yet and would have needed some updates, heavier final drives and heads to get it ready. We did get a 2nd grain cart to keep the machine rolling because of the speed increase. Just my thoughts. Good luck. Matt