UK Car Repair: MGF 1.8, head gasket problem, temperature gauge

Question
I have bought the wife a 2001 MGF 1.8, when it goes over 5000RPM the temperature gauge drops, the car never goes above norma running temperature below 5000RPM and the car does not appear to be loosing water, could this be related to a head gasket problem?

Answer
No I really don't think so.  It is more likely a function of engine speed, ie, the water pump is turning faster, and the voltage, at that speed the alternator would be charging at max and this would likely affect the gauges slightly,it is not a problem and it sounds like you are capable of monitoring it anyway.