that shop is not telling you the truth, The 600 starts making power at 10k and revs out just past the redline mark (I cannot remember what number is there-15.5??). there is definately something very wrong with your bike. You will probably not get to the limiter in 6th (mine would not on stock gearing, have not tried since gear down a bit) but it will in any other gear. I have seen my speedo read over 170 but I don't think it goes much faster than 155 or so.
edit: I just got home and looked at my tach, redline is 14.5, I am sure the tach is optimistic but you get the point.