I think low 1:20 is already a fast time. I got self a low 1:21.
Silverstone is a track with long fast corners, front wing should be high. On the other hand, there are no long straights, so setting the gear ratio to a top speed of 330 km/h isn't usefull. First gear is almost not used during a lap, so extending the first gear gives you a option to shorten 2nd - 7th gear for faster acceleration a higher speeds.
But please share your setup. That's why this topic is here. or PM me to let me test it.
I'm still testing a setup but I finally managed to break into the teens. Got a low 1:19 at one point. Wasn't far hitting 1:18. I've never hit 1st gear on Silverstone.
A rough 1:19.701, accidental pop into 7th at Priory. Only AIDS used auto clutch.