I like to operate between 3,500 and 5,000. The speedometer is not correct and can be off as much as 7 MPH.
Agree with John about the 16T counter sprocket. I have used the 16T with two stock 650 engines, one 685 engine (perfect match), and a couple thousand miles with a 705 engine. The 16T allows reasonable freeway speeds between 4,000 and 4,500 RPMs.
Sustained 85 MPH is not on my list of things to do to a 650, 685, or 705 engine. At 85 MPH you would be well over 5,500 RPMs and I do NOT recommend anything sustained over 5,000 RPMs.
Installing a 685 kit we be recommended if you want to rid your engine (and you) of most vibration and extend the engine life.
2005 KLR 685
2015 Yamaha Super Tenere ES, 5/23/2015
2012 Yamaha Super Tenere; Purchased 7/30/2011; Sold 5/23/2015