Well being that it's only movies, i wouldn't be heartbroken if I lost it all. I have an identical TRM5 going to the same controller with four 750gb disks in RAID5 for data I don't want to lose. the RR2314 was recommended to me from the support staff @ Sans Digital for transfer rates - they said I could see 200MB/s in RAID5 using that card. I wasn't worried about using a hardware RAID card since I have enough machine to handle it. (16 cores, 12GB RAM)
The RocketRaid 2314 is only suitable for RAID 0, 1 and 10. For RAID5 it offloads parity calculation to the OS via driver so it's a host-based RAID solution, i.e. inferior data integrity and speed.
For high performance RAID5 region you're looking at 600-800MB/s under media streaming usage. e.g. DELL PERC 6/i, a server-class hardware RAID controller (performance whitepaper). I'm getting similar performance to their results with my 8x1TB array.
You said you want to use it for RAID0 in a 10TB array, that's fine as long as you're fully aware its purpose and consequence.
Back to answering your question of which stripe size to use, it depends on the RAID controller and the usage pattern. I'd try between 128-512KiB.