Temp on engines is also a matter of preference to some extent:

Most of the recommendations using a temp gun are to keep the engine somewhere below 225/230 degrees. This assumes that you DON'T have the temp monitored during flight but that you fly around, land, and then check the temp between the exhaust bolt and the heat sink (the hot spot on the engine). In flight, you can bet that if you get 195-200 on the ground that you are running somewhere near 250 in flight.
As an example, one of the local fliers has been running his OS 50/MP1 combo for some time now at a very agressive needle setting. We temp'ed him after a good thrashing in his sceadu, and he was at 290degrees! His engine showed no signs of bogging, (through very rough 3d) and had a perfectly thick plume of smoke on 30% nitro. He runs his engines this way consistantly and just rebuilds them as needed, (bearings and an ring).
Keep in mind these are rules of thumb, lower temp means longer life but in some cases, less performance.