Tips on Buying Cars: Lexus Rx350, premium fuel, fuel efficiency

Question
Hey Danny,

We're planning on buying the 09' lexus rx350.  I know premium fuel is recommended but it can use regular too but the fuel efficiency will go down.

I was wondering if anyone knows the MPG on regular fuel and MPG on premium?

If the premium is more efficient, then it will only cost a negligible amount more, but if not then it wouldn't be worth it.

Thanks:)

Answer
I don't know of any sights for comparison, sorry, all I could find out is the following sights, they seem to answer the question better. Hope this helps.

http://www.straightdope.com/columns/041008.html

http://www.consumerenergycenter.org/transportation/consumer_tips/regular_vs_prem...