honestly...on a bolt on car, 65mm is JUST fine. Even mildly modded. If you got the money to spend, Accufab is where its at. As for the Bbk "whistle" its only really a chirp at "tip in" (when you're going from closed throttle to open). I did alot of homework on the quality of them before I bought my most recent one b/c the price was SO right but I'm running a Proffessional Products 75mm on my car. The quality is surprisingly not bad. The only issues I've seen people have with them is the throttle sticks...SHUT. Knock the sharp edge of the blade down with some fine sand paper and call it a day!