Upgrading large 3.1 system to 4.1

We have a large 3.1 production environment.  In our POC run, UMT ran for 48 hours to migrate to 4.1. 

After upgrading from 3.1 Prod to 4.1 Dev using UMT and after validation should we use LCM to migrate from dev to QA 4.1 and Prod 4.1?

Would LCM be able to migrate all the contents (1000s of objects) successfully in one go or do we need to use UMT

to move 3.1 Prod to QA 4.1 and Prod 4.1? 

Using the UMT, the issue is if after upgrading from 3.1 prod to 4.1 dev, any changes/fixes we make to any objects due to breakage in 4.1

we would have to manually make the same changes again if we go from 3.1 Prod to 4.1 QA (and later to Prod 4.1) using UMT.

Using LCM, we can migrate all the changes/fixes we make in dev 4.1 to QA and Prod.

Thanks

Abdul