I doubt a resonably stock skyline would crack 250klms easily.
Remember that the for every k/ph more, the energy is multiplied by four, or something like that.
The average car uses about 8kw to stay at 100kph. 150 would be more like 30 kw, 200 more like 150kw, 250 probably about 300kw or something similar.
A 300kW HSV could only crack 256 at a high speed test bowl in controlled conditions flat out.
Pick any supercar, they are slick through the air, have bulk grunt and the media gets excited when they can crack 300 kph.
I genuinely estimate my car to hit about 240kph with 200 at the wheels. Anything I would be veyr pleased with, but not really expecting to any better than that.
Anyway, I've been wrong once before, but I've never taken my car over the legal speed limit anywhere, so I'm just speculating.
BASS OUT