Can normalisation increase speed?
No, is unlikely normalization will help. What you have there looks more like missing indexes. 29 columns is not much. And BLOB columns are already stored by the system on separate allocation units (out of row), see Table and Index Organization.


  The columns in the where clause are indexed, and reindexing doesn't affect the speed so I assume the indicies are in good shape.


I recommend you read How to analyse SQL Server performance. Your indexes are not used, or not useful. For more useful answer post the exact table definition, all indexes, the exact query, and the execution plan XML.