I'd go for a road bike, you don't need and expensive one to feel a massive difference.
It's far more about geometry and drivetrain than tyres.
Some bikes shops sell nice used road bikes, I'd reccomend going into Glen Parker's in Nedlands if you are looking to get one. They have nice range of new and used, will fit you up properly on the right sized bike and won't rip you off in te process.
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