Welcome to the forum pullinpork!
While I don't have the DBS nor the 6 rack, I have the OBS 4 and can turn out plenty of food I usually finish up in the house oven so as to keep on smoking! At this point in the game its just me and my better half and the kids show up on the weekend for food, and the 4 rack is plenty! If I thought I needed more space I'd probabley get another OBS, which would give me 8 racks for just a smidge more coin.
You'll be very pleased either way ya go, but from what your saying the 4 rack is gonna get ya there! Good luck and keep us posted!
C