hi leco.
There are two independent issues.
(1) How to edit too big content via contentmanager of pico
If you get blank page, it is caused by 'memory_limit'.
Just raise it via .htaccess or php.ini
(2) How to insert too long text into pico's contents table
MEDIUM TEXT allows you to insert 16Mbyte of text.
It looks enough.
eg) this content looks less than 1Mbyte
http://fundosdepensao.com/modules/noticias_financeiro/index.php?content_id=34