I've been concentrating on the Lamborghini and I've discovered that it is very easy to over-drive this car. You can lose a lot of time entering corners too fast and fighting the car all the way through the corner, the excess power is not always your friend. I only started lapping fast in it around Magny Cours GP by not being pants-on-fire, i.e. feathering the throttle and, above all, getting your braking and downshifting done early. You can't steer it by weight transfer like the Porsche. Check your gearing, too and prioritise the corners; Stowe and Copse are crucial for a good lap time at Silverstone GP because they lead onto the longest straights so a balanced corner entry leading to a good exit is key. Don't go in too hot. And see how little rear wing you can get away with, I reckon I'd start at 6.
FWIW, check out my Silverstone tutorial vid here