Like the guy said above.
Too many variables come into play. Like mentioned before air temp, shade or sunlight how hard you drive the kind of soil you run on, and so on.
My engine ( mach 427) usually runs at around 240-260 on most race days, but on some of the hot and sunny days with are temp around 105 F' that we been having here lately and especially this last race weekend, I was pitting for gas and temping at 280-300 with the same tune as the previous weeks race.
I think smoke and sound are the best way to get the right tune out of a engine. My rule of thumb is if its running with a smoke trail and dosent sound like its ready to fly to the moon and you not temping well into the 300 your fine. Unless you are one of those people that like there engine to last mutilpe seasons and 20+ gallons. Then you can tune by temp at around 200 and it should smoke plenty and gas milege should be around 5 min or so.
Another thiong to consider is the typoe of temp gun you use. I have the losi temp tuner with a plug thingy that aligns the temp censor with the top of the glow plug and also i thinig since it cover the top of the cooling head it reads a higher temp then the other ones, that dosent mean its more accurate it just seems more consistent.
Hope that helps.
Dan.