Answer
The gs 350 is less due to it have less standard equipment unlike the gs 430 that has other option. you must also take in to account that the gs350 now has the new 3.5 liter v6 up from the 3 liter it had before. this new improved engine has better horsepower and better gas mileage than before. stay tune as lexus will be move the gs 430 to the gs 460 with in the next year and then it will have more horsepower with a 4.6 liter v8.
hope this helps.