FTS GIN Index Question

Hi List

I have a largish partitioned table, it has ~60 million records in each 
of 12 partitions. It appears that a Full Text Index could speed up some 
user queries a lot.

A quick test with an additional tsvector column revealed that this would 
take up around 35 GB of space for this column and then maybe 5 more for 
the gin index on it. As this is a lot of space (~ 480 GB), I'm a bit 
tempted to use a gin index without the separate tsvector column. 
However, the doc says that this will be slower.

Does anyone have an idea of how much slower we're talking here? The 
index defintion would be a concatenation of two setweights(), i.e.:

... using gin(
   (setweight(to_tsvector('config',coalesce(col1,'')), 'A') ||
    setweight(to_tsvector('config',coalesce(col2,'')), 'B')))

Also, general recommendations regarding full text search configurations 
of that size are very welcome.

Christian