SQL Server Performace After Restart

Hi Guys:

We do restart our sql servers once every month to make sure fail over clustering works.Lately we have seen that performance is pretty bad after the restarts.I am convinced its bad idea to restart the box as everything that is cached gets flushed(sql buffer pool is 500gb).

Can you guys throw some lines on why not to restart SQL Server box;other then what i mentioned.

Thanks,

Viv