4500rpm is about 40mph in 2nd and 60mph in 3rd (I checked on the way home last night) so even if the legal side of things worries you, you can lawfully take it close to the limiter in 2nd on a NSL and still be ok, just watch out for a bit of torque steer and have fun. Dont worry about fuel consumption (what are you getting by the way?), I get 35-37 out of my Cup and see the green gear light fairly often.
The harder you push it the better the car will get over time, if youve had it from new and never hit 5000rpm chances are its a very sluggish Renaultsport.