I bought a new 89' 150 xr4 and was happy with it for 12 years and sold the boat. The difference I was told is that the xr4 has a smaller more streamline lower unit (slices through the water better) Though not as rugged as the regular 150 gear case. I don't believe the props will interchange. As for the qualities of the two I can only speak for the xr4 which was a good engine. I ran it in Ontario 12 years in a row and never failed me except once. I had trouble with the Lund pro-V and they had to send it back to the factory to brace up the transom and when they sent it back to the dealer he reinstalled the motor and gobbed a bunch of goo in the wiring harness plug and it acted as a conductor and the motor wouldn't start out on a big desolate lake. I didn't realy want to try pullstarting that hog so we arced across the starter and got it started and ran back with the hood off. Cleaned out the plug that night and never did it again.
Maybe someone can tell you more about the difference..............Jerry
