table partioning performance

Hi there, we've partioned a table (using 8.2) by day due to the 50TB of
data (500k row size, 100G rows) we expect to store it in a year.
Our performance on inserts and selects against the master table is
disappointing, 10x slower (with ony 1 partition constraint) than we get by
going to the partioned table directly. Browsing the list I get the
impression this just a case of too many partitions? would be better off
doing partitions of partitions ?

Any other advice or pointers to more information with dealing with these
sorts of scales appreciated.

thanks
Colin.