You always hear that when pro's are switching rackets they always use the same racket under a new paintjob which seems logical to me but a lot of pro's seem not worry if they switch string pattern. Ivanovic switched from a 18x20 pattern wilson to a yonex with a 16x18 pattern. Kuznetzova switched from a 18x19 to 16x19. Murray from a 18x20 to 16x19 without any problems. I don't understand this cause it makes a big difference is my experience.