Oracle 9.2 64-bit on Solaris 8

I need more space for a tablespace. The tablespace is currently one 2GB datafile. My question is: should I increase the current datafile over the magic 2GB or add another datafile?

additional info
Unfortunately I have a dB setup using only three logical disks. Two logical disks are RAID-5 (4 physical disks each) and the third disk is mirrored and conatins only the archived logs. I have seperated indexes and data across both disks. We are a hybrid of OLTP and reporting applications.

Than You!