From my understanding, the graphic that shown in the display is rendered by the card it's current plugged in.  You are currently plugged into 6670 that's why it is used for gaming and rendering your desktop.  Try unplug your display and plug to 7970 to see if it works.

Check this: http://www.coinwarz.com/cryptocurrency/coins/litecoin
In the difficulty chart, you can see how the difficulty changed in last 14 days.
It's increased quite a lot, like 30%.
In my opinion, it will at least tripled the current difficulty with in 6 month.

Agreed, If you gather some beta testers, they will help you test your algorithm to see if it exactly works as the way you expected (correct block interval, block amount etc).
Then you can wipe out all the information (or switch to the prod network if you mark the former one as tested).

To gather beta testers, you can offer them some prior time to mine (the not beta tested) blocks before announcement.