Hello
Upgrading the system to a higher version of EHP doesn't mean that you need to scale up the hardware configuration. What really matters and should be taken into consideration is the compatibility of the OS and DB for the target level EHP. The primary requirement is to check PAM for the OS and DB compatibility for EHP6.
You need to get the database upgraded to MSSQL 2008 for EHP6
Upgrading to EHP6 is not going to bring an additional load on the system.
Regards
RB