I am unable to set the default DBMS_OUTPUT buffer size to a value higher than 1,000,000 bytes in View | Options | Oracle | General
In SQL*PLUS the maximum value that can be set for the buffer size is 1,000,000. However it can also be set to unlimited but Toad currently does not allow this.
Upgrade to the latest version of Toad which sets the default buffer size to 'Unlimited'. You can download here.