FWIW, the parts prices are pretty comparable across most makes. And the premium vs regular debate, let's assume you drive 18k per year (your x5 is roughly at 18k per year), average 15mpg, and average a 30cent spread from reg to premium. You will only spend ~$360 extra over that 18k miles running on premium vs running on regular. In my opinion, I wouldn't put much weight into which octane a car runs on when picking a new one considering how negligible the difference is overall.

As far as what to pick, it really depends on what you want to spend. A newer X5 is nice, so are the Cayennes and Touaregs. I'm a big Audi fan but I am not impressed with the fit and finish of the Q7. What about an A8, A7, or A6? Mercedes has a couple nice options for SUV's as well.

__________________
03 3.0i mt
89 325is