OOO was the first overhaul I played with, and I remeber it fondly
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As for other options, it depends on what you are looking for. I'd recommend to read up on OOO (http://tesnexus.com/downloads/file.php?id=15256), TIE (http://www.tesnexus.com/downloads/file.php?id=35265), as well as MMM(http://www.tesnexus.com/downloads/file.php?id=17784), Frans (http://www.tesnexus.com/downloads/file.php?id=2518), and http://www.tesnexus.com/downloads/file.php?id=39202.
Or, if you are experienced with modding, you could try FCOM (http://tesnexus.com/downloads/file.php?id=12249).
To my knowledge, MMM and Frans both support SI.
TIE, however, is very elegant at what it does, it doesn't add as much extra stuff compared to other overhauls, but rather preserves the Oblivion feel rebalancing mechanics and difficulty. It's especially great if you planning to play a thief-ish character. I recently began playing it, after years of having FCOM as a standard install, and I don't think I'll be turning back from it
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You can also mix most of them to an extent, if you are careful, follow their instructions and have some patience with Wyre Bash.