The Titan-Z is literally 2 crippled Titan Black cards with an extra 1000 bucks on the price tag. Gaming wise 2 780ti can destroy it in 1080p resolutions. Since the Titan-Z has actually been marketed towards "gaming" the DP performance isn't that relevant at all. It's a stupid card for stupid rich people, bout it.
The 295x2 is equally as stupid. Just buy 2 of the similar cards for less cost.