Typically Nitro X will give you more RPM through the whole tank.
More RPM = more heat (approx 10deg) is normal.
Experience driver will know Temperature is only a reference, not to judge how a engine should be Tuned.
If your first time using Nitro X, I suggest you Rich the Top needle by 30 mins(half turn) then see engine performance. Then slowly lean back the Top to get a reasonable speed. Once this is achieved, then you should work on the "bottom" needle, leaning it to get extra punch. You will have a Good power, very Fuel efficient and Long life engine.