Its a different engine in the 07 RX350, the 06 model was the RX330. Lexus always use the last 3 digits as engine displacement. The RX350 has a 3.5 liter engine and the old RX330 was equiped with the 3.3 liter engine.
Using premium fuel is a requirement due to the higher compression ratio, not a performance enhancement in itself as many people think. Use of premium fuel in an engine not designed for it will result in a performance decrease or no change at all. :wink: