Nope, 3.6 is as big as it gets. Base models get a 4 cylinder. Even though it doesn't get the 5.3 the 3.6 is a much nice to drive engine and it really feels like 300 hp. I'm not a huge fan of the dual overhead cam, 3 timing chain, over complicated engine, but it does run fantastic when it's all together.
Don't be a hater. You can rent anything, last trip to Chicago we had a BMW 5 series rental and it was horrible.