the user manual for the 650 gives the minimum shift up speed for all the gears. The lowest speed you can shift up into 5th is 25mph - which is pretty slow. The engine would be spinning at 1500 rpm, which is ok if you are just puttering thru a village flat and level with almost no throttle.
It also lists the min shift down speed for all the gears as 15mph. In other words if you want, you can leave the engine in 5th gear with the clutch still engaged (not coasting with it pulled in), and either idle down or brake down to 15mph, then pull the clutch in and shift 4 3 2 1 all at once.
You do not have to pull the clutch in when using the brakes (MC or in a car) until you come to a stop. The little bit of extra load on the brakes will have almost no effect on the brakes if you have the throttle all the way off.
when it comes to engine rpm the thing you need to do is always keep the engine at or above the idle speed (1200 rpm for the 650). The reason is if you let the engine spin slower the oil pump cannot build enough pressure to push oil to all the bearings, and they will start rubbing metal to metal. 1200 rpm is with no load on the engine at all (throttle all the way off). See your manual for the min speeds in each gear while throttle is being applied(ie 25mph in 5th for the 650)...
As far as wearing out the clutch shifting down, don't worry about it. As long as you burp the throttle just a bit as you down shift, the plates will be spinning at the same speed as the clutch disk and there will not be any load on the clutch surfaces.
So here is the real answer to your question - keep your bike in the gear you need to be in if you need to speed up again. For example when I go around a corner from street to street I shift down to 3rd gear before the turn, let the clutch out and go around the corner in 3rd gear. If I needed to abort the turn and go straight, or speed up half way thru the turn, the bike is in the correct gear for the speed Im going. If I left the bike in 5th gear, pulled the clutch in and coasted thru the corner, then shifted down to 3rd then I would have no throttle/speed control all the way around the corner. You always want your bike engaged in one of the gears unless you are shifting - don't pull the clutch in and let the bike coast. Esp on a corner or a curve, because you need to keep applying power to hold the speed steady in the curve, and if you need to straighten the bike out you apply more power, and if you need to make the turn tighter you apply less power.
BTW, if you really want to take off like a bat outta hell after taking a corner shift down to 2nd, but usually 3rd works better for me.
Also do not stop the bike and then shift down into first - shift all the way down before the bike stops rolling. Nearly all motorcycles have straight cut gears and no synchronizer on 1st, so there are gear positions where they would hit teeth to teeth if the output shaft is not spinning, and you would have to push the motorcycle forward or back to get it to drop into 1st gear.
Last edited by KCW; 06-10-2018 at 09:12 AM.