In the front cabin light I left the previously pictured Cree Q5 T10 LED bulb in one map light and fitted a 5 Watt T10 standard type incandescent bulb in the other (I did have 8 Watt T10's in my box of "spares", but went with the lower Wattage. The difference in brightness was huge - a clear win to the LED- so perhaps the 8 Watt incandescent is standard fit?)
I checked the plastic cover of the map light lense on both after 5 minutes for the temperature rise.
Start temperature : both lense ~21 degrees C (within 1 degree of each other)
Temp after 5 min: LED 22.3 C , Incandescent 25.8 C
I attempted to measure the actual bulb temperature, but due to the "glass envelope" construction of the stock T10, the IR temperature gun was giving erroneous readings (around 45.6 C) compared to LED 31.2 C . I tried to remove the incandescent and it was too hot to hold.... My IR temp gun has adjustable emissivity (compensates for different materials IR) but specifies "plate glass" - ie. a flat sheet, not the rounded bulb shape. So I assume that was the problem as 45.6 C would not have made me pull my fingers out of there that quickly!
For the reversing light I refitted a stock 21W P21 bulb and left the other previously posted Cree Q5 bulb in the other light.
Tail Light Reversing Lens ambient: LED 19.4 C , Incandescent 20.4C
After 5 mins : LED 20.2 C , Incandescent 27.2 C
Bulb metallic base temp (after 5 minutes operating in tailight) : LED 65.1 C , Incandescent 177.4 C <- no, NOT a typo!
So there you go.....
I didn't bother testing any of the 5050 LED type replacements - they generate hardly any heat at all (and I'd risk cosmetic damage to those light fittings removing the plastic lens cover for access.)
