The 951 DI is a great engine, extremely smooth and reliable with excellent gas mileage, better than the 800 because it has much more power IMO.
You have to use XPS full synthetic oil with the DI motor. Since it uses less fuel, it relies heavily on the oil for cooling and lubrication.
I've owned both the 3Ds with the 800 and 951DI and the 800 is definitely under powered, not to mention the leaning issue. The DI will pull you out of spins whereas the 800 struggles and 7 mph faster on my gps.