Your old os must be able to work because W10 allows you to roll-back to previous os if it's an upgrade install (although, I haven't tested this). However, regarding Nvidia driver bugs, that's gpu/system dependent. Had I tried to install w10 on my optimus laptop even just 2-3months ago, I would've had problems getting gpu to work properly for what I wanted to test. If I'd done it this time last year, then, for the last 10months or so, it wouldn't have worked properly for gaming and forget DX12 like FH3. 2015 was a no go for almost all optimus owners as well, many bugs os+drivers. This issue has only been solved relatively recently. There are still issues so I wouldn't say it's fully fixed either.