Sure you can save a few bucks by not using premium gas, but you can also save money by not using Lexus recommanded oil, while you are at it, use cheaper transmission fluid, cheap anti freeze and buy the walmart spark plugs, oil filter and air filter. If you dont plan to keep your car for long or if it is a lease then it really doesnt matter.
When you read articles in magazines talking about how people are wasting their money using premium gas, they are talking about putting premium gas into cars that requires 87 octane or cars that merely recommands using 87 for improved performance. As far as I know, the GS350 and GS460 is not one of those cars, it clearly states on the manual and on the gas door USE PREMIUM FUEL ONLY. There is a big difference between premium fuel recommand and required. With the price of gas these days, if the Lexus can get away with using regular gas, that would be a big selling point. The fact that they still require premium gas should be telling you guys something. Good rule of thumb is anytime your engine has a compression ratio of 12 to 1 or more, use premium gas.