It's just a matter of opinion. My wife drives the X5 majority of the time. Once I put the F10 to Sport+ the ride is good enough for me. Also, I have DDC so the suspension does firm up a bit. I may be the only one to say this, but I prefer the steering on the F10 over the X5. The hydraulic steering is a bit too tight similar to the E92 my wife had before. It was a good match on the E92 but on a car as big and wide as the X5, it takes some effort to move around tight spots. I often catch my wife negotiating turns into a parking spot. While the E60 did have hydraulic steering too, it was more forgiving than the E92. I find the F10 be a balance probably due to the fact I got used to the electric steering.
The F10 is also in the luxury mid size segment while the X5 is on the sport activity segment so there's gonna be that difference. It'll be interesting to see what BMW will do with the new 2014 X5 coming out.
I don't think you can fit 315 rears on the F10's wheel well without spacers of some sort.
2013 BMW X5 35i
Alpine White | Cinnamon Brown | M Sport
2013 BMW 550i
Titanium Silver | Black | M Sport