"I might spend similar money on a 7870 or 7950 to leave the option open for dual graphics cards"
No. Crossfire is really poorly implemented. It's one of the many problems and poor design decisions you'll find in AMD drivers. Nvidia drivers aren't trouble-free, but they generally work a whole lot better.
Nvidia spends a whole lot more money on driver development, and the results speak for themselves in the quality of the driver package. Frame latency, multi-monitor, SLI, new title support, and adaptive vsync all simply work more reliably more often on the Nvidia side. AMD makes great hardware, with poor software to support it.
Also, a Z77 that let's you do Crossfire, but not SLI? Check that info again. It doesn't sound right.
"It is my understanding that these can only be seen with slow-motion video."
Your understanding is, again, skewed. Humans are pretty crap at picking up detail, but we are fantastic as detecting motion. Dropped frames are dropped frames. We notice that judder.