What speed of class 10 micro SD cards is optimal for the M8? I'm looking at Sandisk and Samsung cards in the 64Gb variety, with speeds from up to 30Mb/s and 90Mb/s. I'll mostly be using the storage for music. Are the 90Mb/s cards worth it or overkill when it comes to real time performance? I'm okay with slower transfer speeds because I don't plan on switching out 64Gb worth of music often, so when I do I can just leave my phone to transfer overnight. I tried looking on google for any information regarding this to no avail, so sorry if this has been covered before. Thanks for your help!