According to OS there aren't any "correct" temps. You tweak to meet your requirements and as long as there are no obvious signs of overheating (you have smoke and the engine doesn't start losing power) that's the setting you use. After that you check your temp and that's the reference you want to use for your setup. After my "normal" flying (mostly "cruising" around the yard, 80 deg air temp) mine runs around 260 using 20% with a OS 8 plug and set a little rich .