brother, the needle should remain in the middle, anything above that is abnormal.
is your car reducing water also ?
when engine heats up only at higher speeds, it means that something is restricting enough coolant to flow through the engine block. usually radiator is blocked and when engine runs on higher speeds, it requires more water to flow through engine, but blocked radiator fins don't allow enough water to pass through them to cool down engine at that speed, hence the engine heating up only at higher speeds. The solution to this problem is radiator cleaning service.
and while doing that, get it also checked for any leaks, check the radiator cap also if it is okay or needs to be changed.