Started playing cornet regualrly about 6 months ago after 10 years hiatus due to university and young family. Was playing euphonium and Eb on and off during that time. Started on last cornet so fairly quickly got my lip in for two octaves G to G. However difficulty with lip endurance and notes about top G. Now I'm on the front row I need A's. Should I change my mouthpiece (currently Denis Wick RW4) to something smaller such as DW 5? Tried DW 5 and can reach A, B , C fairly easily but I'd have to get used to it as the intonation is different. Or do I just wait for my lips to recondition to the highter notes?