I can agree to a point. Generally, you can not have too many. As far as truck trannies go I prefer a 13. Some like 18's. Others swear by Super 10's. I don't think 10 is enough and 18 is too many. Whether 8 gears is good enough still comes down to the operators opinion. There is no doubt 8 would work. As far as that goes, if the machine starts to lug because you are stuffing the baler faster than it can bale, drop a hole. Sure, it may seem TOO slow and you may want a "tweener" gear, but it is what it is. It may work perfect for Bob, and not for you. My parents have baled for decades with a Ford Jubilee. I would LOVE 8 forward gears.
And Robert.... do you really HAVE to ask why it might erupt?