I think the temp readings are a combination of differing factors, but I think the main factor is the head design.

My Ninja MR21- R01A will not run very good until it hits at least 260F+. At 240F it is so fat it would hardly even shift into second gear. 275F- 280F seems to be the sweet spot for me.... performance, safety and fuel mileage wise.

If you have an Exergen DX-501 be careful..... the sensor window will contact the glow plug and damage the temp gun. Put an exhaust gasket arond the nose cone of your temp gun and you'll prevent it from going to deep into the head.