go to a shop and try them out! mouthpieces dont make you play high! trust me ive been messing around with MP's for the last 2 years and im still no better! playing is not all about playing high although it is fun, MP's only change your sound some help high playing a little yes, ask yourself, 1st question, what type of music are you playing? and 2. what do you want to sound like?
if your playing orchestra you want a big MP, a schilkie 19-24 or a yam 14E or a bach 1.5C etc for jazz you want something a little shallower something like a 3C, schilke 14B-14C yam 14B-C and lead playing you want something shallow schilke 14a4a or yam 14a4a -14b4, bach 3E..... basically bigger MP's give you a softer, darcker sound and shallow give you a brighter sound
the next thing is understanding the numbers, the 1st number the 14 or the 3 etc is the diameter with bachs the smaller the bigger and with schilke's and yams biger meens bigger then the letter is the cup, bachs do a-e a being deep e being shallow, yams and schlkes are the oposite a=shallow basically then rim size, w=wide for bachs, 4 on yams meens wider then maybe another letter etc for the backbore ie. 14a4a 14 diamater, very shallow cup, 4mm rim for extra support and the a- tighter backbore
so think! what do you wanna play! then go to a shop and try them out. with your range top C blowing your head off thing practice lip slurs, scales and arpageos, dominant 7ths were my fav tho
keep practising!