One of the areas where it seems to me that Forza Motorsport rewards you is being smooth on the throttle. Sometimes it's just a tiny application of throttle as you're starting to exit a turn, other times it's going from 30% to full throttle nice and smoothly. Either way, I've found that driving a car with tons more power than grip is a neat way to practice it, and when I raced in the Ultimate GT league I tuned a Merc SLR rocketship for power tracks like Daytona and Road America (my car has an appropriate design with DC Comics' Flash on it, fun for when you fly past your opponents on the straights as you shift from fifth to sixth gear at 175+ mph ).

I chose the Merc since it comes with a supercharged engine that has tons of low-end torque already, and I wanted something that would accelerate quickly. It also has a low stock PI (A652), which I found would allow me lots of upgrades before reaching the league's S800 limit (BTW, the Merc SL65 is a good alternative in this league, it has similar characteristics). What I ended up with is a car that handles quite well in the corners, it has really wide sport compound tyres, but I could also install the race weight reduction. Because I'm not looking for top-end horsepower, the engine doesn't have the camshaft upgrade. That upgrade seems to give lots of HP but partly because it extends the rev range a lot, and this car is all about low-end torque. I also don't install the oil & cooling, nor the intercooler upgrades because they add weight for very little additional HP.

The tune is shared so you can easily use it, but below are the upgrades & settings I used so you can tweak it yourself. Nowadays I'd probably move the brake balance back to 50/50 or slightly towards the front at 52/48, try it out and see what you prefer. Tyre pressure can also be a matter of preference, if you drive cleanly a slightly higher pressure on the unpowered wheels (front in this case) will keep it in the optimal range.

Upgrades:
No engine swap, aspiration swap, nor drivetrain swap
Tyres: Sport tire compound
Tyre widths fully upgraded: Front 275/30R19, Rear 355/25R19
Rims: CXR or equivalent, stock rim size
Drivetrain: Race clutch, race driveline, race diff
Platform & handling: race spring & dampers, race ARBs, race weight reduction
Engine: race intake, race fuel system, race ignition, race exhaust, stock camshaft & valves, race valves, race engine block, race pistons/compression, race positive displacement supercharger, stock intercooler, stock oil/cooling, stock flywheel

Tuning:
Tire pressure: Front 27.5; Rear 27.5
Alignment: Camber -1.2/-0.7; Toe-in: 0.0/-0.2; Caster: 5.0
ARBs: 24.71/24.51
Springs: 771.2/758.1
Ride height: 4.4/4.1 (1 click above minimum)
Rebound: 8.7/8.5
Bump: 6.4/6.3
Brake balance: 48%
Brake pressure: 125%
Differential: Acceleration 60%; Deceleration 10%

Car stats:
Speed: 8.6
Handling: 6.0
Acceleration: 9.0
Braking: 5.9

Power: 787 HP
Torque: 733 lbs-ft
Weight: 3,021 lbs
Front: 51%

Simulated stats:
Acceleration: 0–60 mph 3.185s; 0–100 mph 5.956s
Top speed: 232.2 mph
Braking distance: 60–0 mph 115.0 ft; 100–0 mph 283.4 ft
Lateral Gs: 60 mph: 1.30; 120 mph 1.33