Assuming you are talking about ALL ENGINE performance, it will take you approx 2 seconds to accelerate from V2+10 to V2+18, this is the equivalent of "Improved climb" or "Overspeed", with the slightly higher rate of climb your exposure to the noise monitors should be lower. However, why +18? Why not +20, or a canned speed like 170 or 180?
My assumption is that in the event of an engine failure, you will ignore the noise restrictions and fly as per the AFM.
If you are within the Stage 3 limits, why are you seeking a lower noise foot print? If your attempt is to reach the lower limits of certain airports (Paris), then without certified paperwork to prove these lower limits, the French DGAC wont accept your procedure.
Mutt