Didn't do much for the 250r still the same final ratio as the 85 to 86 5 speeds. Just have to shift more

I assumed they added a sixth gear to the 250, keeping the final ratio the same, to give the rider more ratio options to keep the engine in the power through varied track conditions.  That might explain why the 250, with less torque, would get an extra gear while the 500 would not since it can pull the higher ratios and be less sensitive to larger steps between gears.