The geara on the d9 are under geared for fast riding. The chainring can only be increased 2 teeth to a 56 atb informedd me.
Low gears arw easy on small wheeled folders. Gearing up can be more troublesome. The advantage of ihg is the overdrive.

Shimano nexus 8 is over drive from gear 4 afaicr and a sa 8 is overdrive from gear 2.

If you want higher gears the larger front chain ring option is not an option on a drailler mezzo.
Dual drive gives a decent 36 overdrive and underdrive which is about perfect with a 54 feont chainring