Its been my experience in the past...you want to run the engine at the higher operating temperature like 180+ just because the cylinder head pressure will be higher which will also maintain a more stable compression.....ex. rings will be expanded more. But we (friends at strip) found that obviously you can go to high. I like the 180+ and had no problem running a destroked 400 with 12.5 to 1 compression all day at the track but my cooling system was up to par.