+1 to what Howard has already said ... but 2 more cents ...
What's your upgrade plan? One cannot 'hyperjump' from 1.9 to 2.3,.4.5.6.7. Think beginning .6 memcache was an option with 2.7 it's almost required (at least it's checked for exsistance on the system).
The advised migration path is 1.9.x to highest 1.9.19. Then 1.9.19 to 2.2.highest. Then 2.2.highest to 2.7? Personally, I'd upgrade the current 1.9.x via git to 1.9.19. And continue using git to upgrade to 2.2.highest ... then march it trough EVERY one of them ... 2.3, 2.4 ,2.5, 2.6 via git (might consider holding at that point). Once on a version 2, the git upgrades done via the command line and using scripts found in /moodlecode/admin/cli/ takes very little time.
Reason for the march ... in 2.3 there was change to assignment mod. A new one was introduced. Tool in the Site Admin menu upgrades all of those. Same thing with quizzes/test.
If you catch errors early in the migration process something might be done about them before moving forward. Moving forward without fixing could mean more guruish fixes or loose of data ... or no fix.
'spirit of sharing', Ken