option1:
If you can afford down-time as all projects will be deactive during upgradation.
If something goes wrong; You have back-up and aware of the restore process.
Go for this option, only if you have done several upgradations and aware of the challenegs/knwon issues.
Option2:
Step based approach....Upgrade one proect and estimate the time and understand the challenegs
Any challnegs faced, you can afford to take time as users are still not active on this test environment.
It all depends on size of the data you are planning to migrate.
As such, v10.0 to v11.0 is not as complex as other upgrdations.