Onboard SATA RAID Questions

I'm building a PC for video editing: HD, mostly DSLR based in Avid MC6. I have a stripped-down Dell T5400 that I'm building on and I'm curious about RIADs. My original plan was to install 2x 7200 RPM 1TB Seagate Barracuda drives (separate from the OS HDD in the chasis and use 2 onboard SATA posts to make a RAID 0. I was also planning on adding a SATA-to-eSATA back plate to have fast access to my 2TB G-RAID.
While browsing the internet on the subject I've been seeing reports that the soft RAID config I suggested may not help me speed-wise. I'm looking for some insight. A quality RAID controller card is out of the question right now due to financial limitations.
Should I-
Make a soft-RAID 0 with 2 SATA 1TB drives connected to the MOBO?
Save some cash and just buy a single 2TB 7200RPM drive?
Just stick with the GRAID attached via eSATA?