MAP would provide more power info. Was the MAP about 19.5"?
Also, maybe 80F to 120F ROP would be a mixture setting that would be less stress
on the engine (as might be 40F-50F LOP).
You asked:
What is the "ideal" CHT temp in cruise?
That is like a religious question......... But it depends on a lot of
things. Otherwise, to me, your CHTs are OK.
Some engines make more use of oil in the cooling scheme, such as spraying
the bottom of the pistons. Thus it is more important to ensure oil cooler
efficiency.
New engines run hotter. How many hours on the engine?
Oil coolers are different. Is yours a Stewart-Warner? They have
been shown to be around 30% more efficient than less expensive
competitors.
Then there is the question of how well the air is being used in the area of
the cooler. I am surprised that 10 KIAS slower results in a 10F rise in
oil temp. I know mine rises 20F in the pattern, but that is because of the
poorly placed NACA used for oil cooler air. BTW, I have to partially shut
off the air to the cooler when cruising (always at high power) in an OAT of
0C or less.
Lycoming (I assume you have a Continental) publishes the minimum
oil temperatures that the engine would like to see in the winter - perhaps
Continental does the same.