Redline in 6th is 6000 RPM by default, however you wont have the power to pull it, which is why top speed in 6th is slower than 5th.

 

i have stock 98 stripper m6 i nailed the speedo in 5th and the car still pulled strong. i did also have the window noise. some one once told me that the ls1's have the ridges on hood to let the air roll off and not pull out the window has anyone else heard this. the guy that told me also had the 9 sec car back home that no one ever saw