The wing is identical between 330 and 340. As for performance, well a 330 will get there quicker (though a 340-600 will get to 370 with a full load (58t ish) in around 26 mins eastcoast bound); for a similar thrash across the pond with a full load (35t) the 340-300 will go straight to 370 ex JFK, (and 360 ex LHR. ISA conditions). Slowly though, about 34mins for a C2 powered a/c and 29mins C4.