"Breaking in" headphones is a myth. Your subjective listening preferences adjust to the headphones that you use. You may get a more comfortable fit as the band and cushions conform to your exact shape, but the performance of the drivers isn't going to change significantly.
I have been well-pleased with all of the Sennheiser headphones that I have purchased over the years, including the very well worn HD430 set that currently serves my PC gaming & music needs.
i7-6700K, NT06-Pro, GA-Z170N-Gaming5, 32 GiB, RX Vega56, SM951, 5TB HDD, Blu-ray, FTZ01, SX800-LTi, C32HG70, RK-9000BR, MX518