Anat, there are some issues with 12 SR1, so don't install this release for now.
QV12 IR seems to be working fine, though.
Regarding the upgrade process, I am not sure if there is an update to existing QV upgrade and migration document you can find here in the forum, but in case you don't find an updated one, go through the old version and the current release notes.
The new engine should be able to handle large amounts of data at good as the old one, maybe better.
See Henric's comments here on some internal changes