Okay, so first thing to do: Always, ALWAYS, enable USE_MAXSP_LIMIT from HandlingFlags. It makes the defined top speed to be accurate and makes the vehicle actually try to reach the top speed. And, just for comparisation, here's my own handling I've made for BMW 1M:
CADRONA 1495.0 5225.0 1.4 0.0 0.12 -0.07 -1 0.49 0.87 0.47 5 293.0 29.5 72.0 R P 2.2 0.54 1 41.0 0.7 0.3 0.0 0.11 -0.04 0.5 -0.2 0.40 0.54 47100 C0002000 5400000 0 0 1
As you see, I'm using bigger drag setting (car isn't really aerodynamic), top speed is slightly less than 300 km/h, BUT: My acceleration is higher than in your handling. Same with engine inertia. Even with that "high" acceleration I'm using, it's really hard to reach top speed and nearly impossible without nitrous. I've used high engine inertia to allow smoother acceleration. Remember always check any handling flag there is, they affect really much.
If you want to have really realistic handling, you should adjust acceleration so you can barely reach top speed, and then set engine inertia for smoother acceleration. After that, tweak suspension* and grip and you're good to go!
*Though suspension also affects grip, and in some cases, also acceleration, so you better make suspension somewhat working.
EDIT: Almost forgot, if you need good speedometer for temporary use, I'd recommend my Digital Speedometer, compact and supports both KM/H and MPH. This post has been edited by oksa8 on Sunday, Jul 8 2012, 09:56