Correct me if wrong, but I believe the Octane PVO doesn't offer compression, only I/O, whereas the O2 does hardware MJPEG compression. That means you'll need a fast disk setup to do realtime capture on the Octane, and video will subsequently need to be compressed using a much slower software method, preferably after transferring it to a Mac or PeeCee. The O2's realtime compression yields decent video quality and can be ported across platforms, a few quirks aside. Overall, the O2 would probably be more convenient as a capture platform.
Regardless, any respectable O2 should have the A/V capture board, so yes, spend the extra $10 for it.