You can always run taller tires if you don't want to switch 5th gears (that's part of why a lot of high HP drag cars go to 26" tires besides better availability).

I have the 25% taller 5th gear (for comparison, Evo 3 is about 10% taller than stock) which is what you want if you're really doing top-speed runs.

Or like Paul said - you can rev out to 7.5-8k+ in 5th and get not that far off the magical 300kph mark.