We try to educate our posters all day to mantain posts clear and usefull...
I don't know how to resolve this problem...maybe the best solution is to hack the modules...or talk with my provider...
What did you do to have such a big database?
Analyse the size of your tables with phpMyAdmin.
The load is only distributed, if the databases are also placed on another server.
By placing some tables on another database only some queries are diverted eg if they belong to a module, then it is only the case when the user is visiting that module.
Not sure what your rationale is with this approach.
2) try to use MySQL Engine MERGE