I agree. The 955 could handle the 6ft blade but the 5ft will be more manueverable. I had a 6ft on my 2720 for a short while as it was left over from my Ford 9N. It was a bit unweildy. I sold it and got a 5 foot and am much happier.
The only thing you need to ask yourself is do you plow a lot with the blade angled? If so, you want the blade to still cover the width of the tires while angled and you might need a 6ft blade to do that.