The KK blade I have is 6 foot. I am not sure of the weight. The tractor will lift it fine. The problem is when you are dealing with 6" or more of snow. The blade acts as a rudder and will want to turn your tractor. Since the 2210 does not have separate brakes you will be fighting keeping a straight line. I ended up trading with a neighbor that has the L3000 kubota. He had a 5 foot blade. During the winter he used my 6 foot and I used his 5 foot. The 5 foot just seemed to be a better match for the 2210.
I have a 5ft RB for my 2210. I agree, when plowing heavy snow 5ft is enough. I have the FEL on and 100 pounds on each rear wheel, so traction isn't a problem, but a 6 footer would probably "overpower" the tractor in heavy going.