Gonna step it up to a -10. I dont see the need for any thing larger since the oil filter adaptor is 1/2" and the pick up tube is 3/8". How would using larger hose on the cooler improve any flow when the pick up is smaller? Can only get so much oil thru that 3/8" pick up. _10 is .530" id. Should be more than enough. I would like to hear from anyone that had a failure using anything smaller than -12 hose on their cooler system.
At one time I had a Jaguar XJ6 and the oil cooler lines where in the range of one inch or so and I'd bet money the pickup in the pan didn't come close to that.
There's also gonna be a parasitic loss pushing oil down those smaller lines.
