go with a chopper. We have had a kirby spreader and a redekop chopper on ours and the chopper is way better at spreading. We would often overload the kirby and slow it down, causing even worse spreading
I should warn you that the literature overstates the capacity of the extension. The literature says the flared extension adds 100 bu and the tip up adds 45 bu. What the literature doesn't recognize is that to add the flared extension you have to remove the flip up extension that comes from the factory. You lose 60 bu when you take off the factory flip up extension so the flared extension really only takes the factory hopper from 240 to 280 bu. Adding the 45 bu tip up gives you 325 bu.