For a top speed tune, you need two things:
1) A first gear that you can launch without bogging.
2) A long enough transmission without topping out.
Try flipping the transmission at maximum final gear(ie. 5.000 or 5.500), then set the top speed slider to lowest top speed, then drop the final back down to lowest(ie. 2.000 or 2.500). This will stretch out the tightest gearset to get the best shifting possible for a long transmission. If you can't launch with first gear far left, adjust the gear so you can launch. If the transmission isn't long enough, use a higher top speed when you flip the transmission. Adjust your gears between but try to have 4-6th far right on the sliders.
For the suspension, you need to set all camber and toe settings to 0.0. Anything on these will cause you to lose top speed and acceleration after ~200mph. Ride height should be maximum on both, and spring rates/dampers set at your leisure according to whether it will be a semi-circuit tune or full out top speed, but hard rear springs will give best launch.
I'm feeling generous today, so enjoy the advice and see what speed you can make your Cien achieve.
