use whatever 5th gear ratio, diff ratio, tyre size, and rev limit you've got/want

Top Speed Calculation Example

Tyre Circumference (for 225/35/17) = pi x diameter
= 3.1415 x 589mm
= 1851.34mm
= 1.85134m

Now 1 mile = 1609.344m

Tyre revolutions per mile = 1609.344 / 1.85134
= 869.286

Engine revs per mile = tyre revs/mile x top gear ratio* x diff ratio
= 869.286 x 0.82 x 4.44
= 3164.897

* TKO gearbox

Now, engine revs per hour = 7800rpm x 60
= 468000


Thus top speed = engine revs per hour / engine revs per mile
= 468000 / 3164.897
= 147.87mph

With 225/40/18 sized tyres (with 2m circumference), top speed = 159mph