What are the most unaccomplishable games for you? I have some ideas, such as Liferaft:Zero or MoneySeize. But even if I gave up with both of them I got much further in Liferaft than in MoneySeize. So i vote for MS.
Perhaps with a perfect coordination they can all be finished. How about building some player program. No cheating, rules respected.. just the perfect player for every game. This should prove everything.
Of course they're really hard, but there are some too hard hard modes of many games that I can't get past. For example, Expert Mode in Giraffe Attack, or Insane Mode in Run Elephant Run.