You're welcome, Marten -
I don't think the data transfer rate through HDMI is the issue... that data is the highly compressed and difference-encoded AVCHD stream from the camera.
What matters is the data rate that needs to be written to disk, after the stream has been demuxed and transcoded into whatever codec you plan to use.
I did the math on a few of my TD10 files, all of which are 1080i 59.94.
Files encoded as ProRes 422HQ single-stream are about 27MB/s, which means 54MB/s for stereo.
To my surprise, ProRes 4444 files are roughly the same.
For comparison, uncompressed files are 127MB/s, or 254MB/s for stereo. My 8-drive RAID tops out at 414.9MB/s write, 256.7MB/s read. Remember, you'll need to be able to cover the bandwidth for read as well, for smooth playback. (None of these figures should be taken as gospel; they're just the results I'm getting on my system.)
I double-checked, and that fire engine image I linked to was actually ProRes 422HQ, not 4444.
You can test your system's capabilities using this handy free app...
http://itunes.apple.com/us/app/blackmagic-disk-speed-test/id425264550?mt=12
Note that the results it gives for success in different formats are for *uncompressed* files... if you're using ProRes, you'll actually be able to capture in many formats this test marks as failing. You'll need to compare the actual numbers you get from the test with the numbers I've shared for comparison.
I hope that helps!
Randy