I think :
a) a short look on the init.ora-params,
for examples db_blockbuffers = 4096
log_buffer = 64000
are set for a playing-db

b) a short look on physical things
size online-redo
sharing of disk
rolbacksegments,
...

c) THEN LOOK after poor SQL-Stmts in V$sqlarea, something like TOPSQL, 90-95 % this is the reason for poor performance.

Orca