You have to take into account that the fifth gear ratio is not 1, but rather for the S2:

1st 3.15
2nd 1.91
3rd 1.28
4th 0.95
5th 0.76

So the total ratio at 5th will be 0.76*3.82 = 2.90

The available BC gearbox final drives are 3.58, 3.82, 3.84, 4.27 and 4,29.

Once one has enough power (200+) the close ratios don't affect the acceleration too much anymore. It might even become the opposite.

Anyhow a 195/50-15 tire will have a rollout of:
3.1416*15*0.0254m+2*.50*0.195m = 1.810 m
and at an engine speed of:
6500 rpm = 39000 rph
will have a theoretical 5th gear speed of:
(39000(1/h)/(3.82*0.76))*1.810m = 243400 m/h = 243.4 km/h