Ive just finished running my Impreza motor in.

10w 40 Millers running in mineral oil for 50 miles. Drop the oil/filter
Same again for another 450 miles, drop the oil/filter.

At 540 miles i swapped to Motul 300v. Now done 650 miles and mapping for full power this week.

I was running boost through the car and up to 5.5k rpm within 8 miles of start up.

Dont go all softly softly on run in. Give it plenty of load and at very least 0.3 bar boost.