How to accelerate full-text search?

[Roman Garp]

Hi!

I have MyISAM-table with 3 000 000 strings. I've built the full-text index on 1 column. Now, then I search words, which appears seldom in the table, they finds very fast(0.05-0.2 s). But frequently occurring words finds more slowly (20 - 80 s). I use simple query:

select filename from file where match(filenametext) against('"simple words"' in boolean mode) limit 0, 50;

How can I improve results?
Thank you and sorry for my broken English.

System configuration:
Red Hat 9, MySql 4.0.18.

Computer:
P3 1.8 GHz, 512 Mb.

My.cnf:

key_buffer = 256M
max_allowed_packet = 1M
table_cache = 256
sort_buffer_size = 1M
net_buffer_length = 1M
myisam_sort_buffer_size = 64M
thread_cache = 8
query_cache_size = 16M
default-character-set=cp1251
ft_min_word_len = 3
ft_stopword_file = ''

record_buffer = 1M

[isamchk]
key_buffer = 128M
sort_buffer_size = 128M
read_buffer = 2M
write_buffer = 2M

[myisamchk]
key_buffer = 128M
sort_buffer_size = 128M
read_buffer = 2M
write_buffer = 2M

[mysqlhotcopy]
interactive-timeout