Hi Will,
I have a 2007 RX350 and have now done 42,000Km. I have not had one problem in that time, a very well put together car, in my opinion. Not sure if this will make a difference, but I think you will find most US RX350's are made in Canada, and the Australian ones are made in Japan. Most of my driving is on highways, freeways etc. and consumption for this sort of work is around 9 to 9.5l per 100km. On the brief times I drive a lot in the city it is around 13. The power is certainly adequate for nearly all types of driving.
Hope this helps
Cheers
gripper