I see mention above power outputs and how this is a factor for top speed....
Ok on a race track like eastern creek, yes this will help you achieve a higher top speed at the end of the straight... But on a perfectlly flat straight road like a salt pan... (controlled conditions) The power of a car has absolutly no factor in top speed (other than wind drag) but it all comes down to ratios...
Like a said above a dyno is the only way to confirm top speed. Because there is no wind drag on a dyno. Power will get you to the top speed faster yes, but will not increase that top speed. Considering you have a rev limiter, if you bounce the car off it in 5th gear youd get to around 267kph by my calculations. The guys at the local dyno tuning shop said it would be ir-responsible to test this on a dyno cause it would be very dangerous, he said speeds over 220kph could dammage an average dyno.
So i guess its impossible to tell. Take the air strip for instance, a tail wind would help in achieving a greater top speed then going into the wind. However in this case more power would help going into a head wind in achieving a greater speed over a stock 33.
This logically. 7000rpm is standard redline on a 33. At 3500rpm you can be doing about 134 acording to many dyno print outs i have seen. So double that figure. 7000rpm would be roughly 2 x 134 = 268kph..... Take an extra couple of rpm till rev limiter kicks in then you may be able to achieve 275 or so....
I have put a lot of time into thinking about this topic and i appoligise about the "flux cap" comment above but i was in a joking mood....
Anyways in conclusion its all about the drivetrain ratio.....