Speedometer Error

Hi all

I have a GU Nissan Patrol and originally had the standard wheels and tyres 265/70 R16 and at 100 km/h on the speedo i was actually travelling at 91 km/h.
So i changed tyres to 265/75 R16 and still had about a 5% error, 100 km/h on speedo and actually travelling at 95km/h. (note: speed measured using GPS)
Now the current sensor gear has 15 teeth, i would like to know wether i should go down to the 14 tooth gear or up to the 16 tooth gear.

Thanks a lot.