In terms of performance not sure, depends on your machine and water detail settings, I usually like enhanced water but that really should be used with high detail and the SI version which is only high detail.
Theres been an update recently to Phinix Water which is good, now supports SI if you have it installed and probably better performance wise, have a read of the description and check out Vanilla v Modded screenshots....
http://www.tesnexus.com/downloads/file.php?id=6680
Other water mods, havent looked at these for a while but see which suits, some too clear, some too blue, your choice though....
http://www.tesnexus.com/downloads/file.php?id=2734
http://www.tesnexus.com/downloads/file.php?id=12763
http://www.tesnexus.com/downloads/file.php?id=2168
http://www.tesnexus.com/downloads/file.php?id=3082
http://www.tesnexus.com/downloads/file.php?id=26145
http://www.tesnexus.com/downloads/file.php?id=32261