As you may ot may not know, speedos are very inaccurate as you gain more speed, and, as a safety feature they overread
Not only that, but change your wheels and tyres and this also has an effect on your speedo reading.
Sooo, heres a top speed calculator - this uses your rpm, gear ratios, and wheel/tyre sizes to work out your genuine
top speed and not an over reading speedos top speed.
There is however inaccuracy in your rev counter too (Though not as much as the speedo) and these also tend to over read. The only way to get a true rev readout is with a direct connection to ECU which reads on the rpm output wire - the apexi stuff is very good for this:
As a good example, my old 200, if you went by the speedo reading did 180+mph
, however I hit the limiter in 5th a few time in it and this was set to 7200rpm - even though the rev counter read near 7500. Actual speed was 165mph with a reading of 7190 taken on an Apexi AVCR and Super AFC - this kind shows the inaccuracy in the speedo and rev counter.
Anyway, heres the Calculator - have fun http://www.race-technology.com/WebPage2/Other/Utilities/GearCalculations/GearCalculation.html