This pops out one physic feature of game, yes there is mass counted for Drivetrain, clutch(flywheel) and tires. How much torque goes on clutch depends several things, and rpm/speed of car. Places where game counts slippage are clutch and tires, if you have time to test with data logger you'll see logical reasons for speed advantage. On certain point slipping changes to other way, just because of torque used on clutch vs gear(on box). There is few percentages slippage on clutch, 12000 rpm engine it easily make differences of 300rpm between that type gearing. Yes longer final (2.500) will give higher top speed, but it also makes cornering ability weaker/fragile when tires aren't giving good grip (i.e. Comfort grade tires). (But not on all gears giving higher speed.. ) That inertia has a role in game, and it's counted in game physics engine. One "prophet" said at there is absolutely zero difference between clutches... Dah.. Approx second per clutch when tried Caterham 7 on Tsukuba, carbon drive shaft gets half second also.. About Caterham, it's good for testing low torque engine, but should do test on opposite too and pick high torque low rev engine, engine without turbo. Engine brake is applied soon as speed is declaring, I'm not speaking about braking engine, I'm speaking about engine brake. Amount what engine resists Drivetrain+wheels when i.e. Lifting throttle, that's activating brake side lock, always.