45+ MPG is excellent! You've increased about 1/3 over your previous 35 mpg.
A ScanGauge would provide near-instantaneous mpg display is a good idea if your car is OBDII. I don't know if OBDII is available only on USA cars or also other markets.
Or, with your background, I'd guess you could build an MPGuino. You'll find threads on that here in the Instrumentation sub-forum.
OpenGauge / MPGuino FE computer - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
If you haven't done any mods yet, you could take a look in sub forum EcoModding Central, the sticky [Master list of 60+ proven mods for increasing MPG].