Oracle 81.17 on solaris ..
I my app at 100 users load ... I have following stats
each users fires 7 similar queries on db
db response time for single user - 160 millis
avg db resposnse at 100 - 2 secs
queries on average result 100 rows ...

Library cache get hit ratio ; 96 .60
redo spacce wait ratio ; 0.6429
rows from index/total rows; 2.0659
buffer cache hit ratio ; 99.9702
directory cache hit rate ; 98.3299
directory gets ; 71315
directory misses ; 1191

where s the bottleneck ?