I say you make root filesystem about 20GB and rest all.
Also ext family of filesystems let you keep some space for 'root' user as an emergency in case of disk full condition.
It is set while making or afterwards using 'tune2fs' utility.
mke2fs -m 5 /dev/sdx
tune2fs -m 5 /dev/sdx
Change in above '5' to your required percentage of filesystem space to reserve.