I am not sure but there is no SystemPartitionSize parameter, only parameter is WindowsPartitionSize. WindowsPartitionSize is used to specify size of system partition in GB ,ranges from 20GB to 100GB. If not specified then default is 60GB.
I seen threads elsewhere that said to use WindowsPartitionSize=MAX and some other site says the limit is 104132 = 104GB what does the MAX do? set the C: to 104gb? I might have to do some trial installs to find out if no one have the answer.. thanks