FULL TEXT MEMORY USAGE

Hi
I searched everywhere to find sth about memory usage of full text tables but I couldnt find anything .
I have a larg table with 277,000 rows all with medium lenght text data . I use full text index on the table . My index size is sth about 650MB AND there is more than 200000 select queries daily .
The question is how much ram does full text index use ? As my search queries are really small amount compared to other queries and all are limited to users with about 100 to 200 rows (using where clause), Will Removing full text and using like improve my database performance ? I am ready to even remove search function ! Because performance is more important .

Thanks

Full-text indexes use the normal MyISAM key cache.