New BI7 Upgrade Strategy..Help Needed

Dear Gurus,

Client is planning for an upgrade to BI7. We are in the process of evaluating the time lines and effort required. If anybody worked on the BI7 upgrade from BW 3.5, please share your experience on coming up with an effort estimation and time estimation. Please also share your experience on what all need to be considered before doing the upgrade and after the upgrade.

Regards

Vijay