I've given the Murasama (too much Touhou games lately make me misread that as "Murasa-sama") and the Furia a shot at their suggested courses, here's some thoughts from me. I use Logitech Driving Force GT wheel with the default 200 degrees steering lock, as these are open-wheel race cars that demand twitch reflexes.
Murasama @ Milky: Is this car supposed to be driven flat out here? I think the gear ratios are rather too short even for single-car runs. Too bad this track's front stretch and Turn 2 rape my frame rates...
Murasama @ Long Pond: Feels okay. Probably should stay with a bias toward understeer so it's drivable in traffic, although it could do with a graze more downforce for this track in my opinion.
Furia @ Corkscrew: I think there's a simultaneous problem of having too much peak grip and having it drop off way too fast. It's far too easy to overdo correcting a slide, because everything happens within tiny fractions of a second. Some yaw tolerance at mid-low speeds would be appreciated. I understand that this is a top-end open-wheel race car armed with a turbo'd 850 horsepower V-8 and negative lift many times its base curb weight at high speeds and cutting-edge racing slicks, but the setup is far too unforgiving. I can do 1:11 times, but it's very inconsistently doing so. This car is kind of like Illya from the Fate-series of visual novels: If you stay far away from her limits, she plays nice. But if you push to the limit, she'll brutally murder you in a blink if you're not quick enough to react.
Again, I don't think it's the amount of grip that's the issue here... it's more a matter of having to react both insanely quick and with such nearly impossible precision.