I had the x6 35 before my current x6 50. It's actually a tough call

50i PROS:
- Sounds incredible
- Serious go

50i CONS:
- Sh***y gas mileage. Averaging 12mpg now vs 16-17 then (admittedly only got 800 miles on new one, so still running in)
- Not convinced handling is quite as surefooted, as the weight balance is different. With a load in the trunk or rear passengers tho it's a wash.

I prefer the 50i, and always (ever so slightly) regretted not getting it last time, but either is an incredibly fun car to drive, unique, and fairly practical to boot.