Lower it? 4K RPM at 70-75 is almost lugging the poor thing as it is.. at least that's what my '08 does.. and that is where the sweet spot in the mpg curve is.
I suspect if you lowered it much with taller gearing you'd be adding quite a bit of torque strain to the engine bottom end unless you are planning a bunch of coast to coasters where you will need or want only minimal power at speed with stops only for fuel..

Or are you trying to sneak on some more top end speed?
IMHO the Norge gear ratio's are about perfect.
Smarter minds than mine may offer more realistic opinions..