I have a well made Taiwanese model that is 8" x 72". I plane a lot of rough lumber and the wide and long bed jointer is a must for that. I would have had issues with a 6" width a few times but I can't remember the 8" width not being enough. Someone posted a formula for how much the length of the bed limits the length you can put over it but I can't remember what that was. I would say that it was 35- 50% longer than the bed length as an educated guess and based on experience.
If you are doing a lot of lumber and especially if it's rough lumber then you need a big floor model planer. Mine is a 2 hp King Canada which is also sold as Delta, Jet, and a few other brands. It's 16" wide and will take 1/8" bites all day long. Some planers have rollers on them to make it easier to pass a board back for a second pass. But you need a second person helping you to take advantage of those. I do mine in batches where I'll run a half dozen or more boards at a time so that I'm not constantly winding the planer up and down and so that my finished size is the same for each board. So for that I set up sawhorses on one side of the planer to stack the boards on. Needless to say you need a lot of room for that.