Trying to Run Windows 10 on Flashed Mac Pro 4, 1 now 5, 1 Bootable USB Storage Error Bootcamp

I want to run Windows 10 on my flashed 2009 Mac Pro 5, 1 with Bootcamp. Currently OS X 10.11.6 and the Nvidia GT 120 are present. I am able to start the process to create the bootable USB drive but every time the progress bar stops midway and says that there is not enough space on my USB drive. The USB is 123GB and completely cleared. The Windows 10 ISO is around 6GB. I have also tried reformatting it to FAT32 and exFAT, with no luck. I have also disabled Time Machine and automatic backups. Does anyone know a fix to this or should I just install Windows 10 via DVD?