Oracle index on column with length > maximum varchar2 length
I think its a good suggestion done by @raj moving to 12C as 11g is nearing EOSL.
If you are considering using CLOB with Oracle Text Search, consider below.

Maintaining Indexes and Synchronization
In 11g users can specify at index creation the index update preference: manually,
on commit, or at regular intervals. Users can also specify a transnational text index,
where documents are searchable immediately after being inserted or updated. Note
that the catalog index type - designed specifically for the short pieces of text
typically found in eBusiness catalogs – is always transactional and needs no
synchronization. 

Pleaese read: http://www.oracle.com/technetwork/testcontent/11goracletexttwp-133192.pdf (Page 12)