I ran WAAS for a couple years planting 12 and combining 8. Moved to RTK the past couple years and it makes a big difference. Big enough to pay for the upgrades.

The biggest thing I have found with planting 12 and combining 8 is at the end of the row. Give yourself plenty of room to turn around and get the next pass good and straight, even if you have RTK. That will eliminate the guess rows being to close or too far apart and knocking down plants/cobs.