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.