opc.three (3/27/2013)
At 50% I would rebuild. If you're having trouble with log size look into partitioning your table and indexes so you can rebuild smaller subsets of your index, ie only the partitions that need it.
Or switch to bulk-logged recovery model if possible.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability