This is just my personal experience: I installed a factory new 390 a couple of years ago (under the then Lycoming experimental program). After the prescribed break in flights, my initial oil consumption was relatively high. Prior experience with breaking in 360s was that after around an hour of full power flight the CHTs would drop noticeably, and oil consumption after break in would drop to decent low levels quickly. With a little bit of alarm, I discussed this with Lycoming and was informed that with the 390 series a new type of substantially harder oil rings were being used, and they break in much slower. I was advised to keep running break in oil until the consumption dropped and stabilized and expect that to take up to 50 hours. In my case it was 75! And even after that, the oil consumption kept dropping a bit more over time, and has converged to around a quart in 10 to 12 hours. Aeroshell W100 consumption is noticeably higher than Phillips X/C. I'm not totally happy with this level of consumption, but have been told it is OK for the 390 and at 450 hours now my compressions run 79/80 to 80/80! So, I guess I am happy...