Hi Raj,
If you are upgrading because of some issue which is affecting the Production environment and the fix is to upgrade to SP5 then you I think you should go for the upgrade, however if its not the case then you can wait for SP6 and you can also go through the Merlijn post about 'Whats new in BI 4.1 Sp06' at the below link
Regards,
Shreejith