If you're looking for a quiet, completely road-isolating car, the 6 isn't it. At cruise, this is one of the smoothest, quietest cars I've ever ridden in. When provoked though, the motor lets you know its there.
I never drove a Camry when considering buying the 6. Two completely different personalities, and I doubt many Camry lovers would swap for a 6 & vice versa.
I had a Camry v6 as a loaner for a week, when my dodge stealth was in the shop. The 6s is definately louder at high RPM, though not by much. The real difference is the suspension. The camry felt like a boat. The 6 is almost as firm as the stealth.
Personally, I love the way it sounds when it's cold. The first few minutes of driving are a little louder than normal driving, but it's a very nice tone that I wish was there all the time. Very aggressive with out being intrusive. My room mate has told me on more than one occasion he doesn't mind being awaken every morning by the noise of me leaving for work in the morning. His girlfriend, on the other hand, isn't so forgiving about being woken up Tire squeal is optional.