The 650´s are geared a little low but the engines are designed to run fairly fast without doing any harm. I usually ride about 70 with no problems and have 23000 miles. I know guys who ride them at 80 all the time and have 50000 or more miles... one guy like that has 80,000. If you drill holes in the baffles you will hear a nice low sound that will make you realize that the engine is doing ok even at 75 or 80. It is the whining of the lower engine parts that you are hearing that makes you think it needs to shift at 55.In fact I usually don´t shift into 5th until 50 or 55.