The Final drive differential crown wheel/pinion gearing on your AYR gearbox is 71/18 which gives a ratio of 3.9444 to 1
which will give 2744 rpm at 100 kph or 36kph per 1000 revs

Your 5th gear ratio is 34/45 which = 0.7555
which is the same as the 02A AYN 2wd gearbox

The AYN gearbox has 70/19 which is 3.684 to 1 –
which will give 2560 rpm at 100kph or 39 kph per 1000 revs

You can work out your speed & revolutions from these figures here,

http://www.scirocco.org/gears/

Tyre diameter & circumference here

http://www.miata.net/garage/tirecalc.html

previous post amended

1000 rpm = 41kph
100 kph = 2387 rpm

btw all calculations have been made assuming you have 195/50-15 tyres fitted.

Specification – Sidewall – Radius – Diameter – Circumference – Revs/km – Difference
195/50-15 — 98mm — 288mm – 576mm — 1810mm

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553

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0.0%
195/45-16 — 88mm — 291mm – 582mm — 1828mm

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547

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1.0%
185/55-15 — 102mm — 292mm – 584mm — 1836mm

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545

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1.5%

The rolling radius difference of 1% to 1.5% is not really worth worrying about, as it would only give a speed of 101 or 101.5 kph at same 2387 revs

Before someone misunderstands me,(not you Dan) all 4 tyres must be the same size front & rear!

No one thought that you/it were dead, just very quiet []