The settings you used for the Subaru would help too.
I didn't really do anything special for subaru. I upped the power the maximum allowed, I lowered the weight to the minimum. I added a wing to it before I attempted the race for the first time, however I don't think this is advisable because it understeers enough without it. The first time I ran I got within 2.5 seconds of the leader, however I went off on the last corner on the first lap which cost me all that time. The next time I did it i bought the tuneable suspension which I then lowered, made the rear stiffer and the front softer, while adding some camber. This made it ever so slightly better but I wasn't faster with it so it's not needed imo.
One piece of advise I would give is to watch the Jackie Stewart topgear piece, specifically the part where he goes into 'yoda mode', where he pushes on James' shoulder. This car does not like direction changes and it has no added rotation when turning like an elise does, so you have to ease it into the corners slowly to overcome the understeer, and you are punished serverly for braking too late so avoid that. When I did it, I was braking before he ideal braking point and gently coming off the brakes before the corner to make sure I didn't overcook and lose a lot of time.
The Elise challenge I found really easy, all I did was up the power to max and add a racing gearbox and clutch. The car is so good to drive, you only have to think about turning and it will turn. The fiat 500 one I did first try after adding a low rpm turbo and detuning the engine and different gearbox. The gearbox doesn't matter though, because the power curve is flat from 2500/3000 rpm or so, so the gearbox is giving no advantage.
Hopefully that helps, I'll video the replays later.