It's nothing to do with your vehicle speed, the gearbox doesn't need running in. It's the engine speed you want to be mindful of.
Keep the revs below 3000rpm but don't be scared if you stray over that for a little while.
1000 miles is a good figure to aim for.
Always drive calmly until the car is at full operational temperature before giving it some power, if you have a turbo smart, drive calmly for 2 minutes before you pull up and turn the car off to allow the turbo to cool.
To be honest, I doubt it will make much difference, fully synthetic oil is terrible for breaking in an engine.