Someone with experience tell me how well SLI works. I might very well get a 660Ti, keep that for a year or 2, then buy another for SLI. However I know crossfire has been very sketchy when it comes to reliability in a lot of games. Heard stories multiple times about just having to flat out disable crossfire to be able to play some games, and beyond that, games just not running very well with crossfire. Almost every Catalyst patch includes multiple "this game will perform better with crossfire" patch notes, which leads me to believe when new games are released they almost never work that great with crossfire until the cards drivers are updated. I have heard some complaints about SLI scattered throughout the interwebs, but not as much as crossfire. Tell me, how well does SLI work, is it pretty much in the same boat as crossfire considering they use the same techniques? Is it worth it to eventually SLI, rather than buy a beefy card from the get go like the 670? I've already read the SLI/crossfire faq thread, but it didn't give me exactly what I'm looking for. I want personal experience for the most part.
CrossFire has made lots of improvements over the past few years and is a very good solution. Both nVidia and AMD release their latest drivers with improvements for multi-GPU
scaling for AAA games.
In fact, as of the latest drivers for AMD (12.7), Radeon cards seem to scale better in terms of performance, which only makes sense, since AMD's strategy has been to build smaller, cooler GPU's and build multi-GPU cards, each of which uses Crossfire. So in my opinion, right now Crossfire is actually slightly better then SLI, at least until nVidia releases it's latest drivers.
However, SLI is still a terrific solution, and on it's own the GTX 660TI will probably kick tremendous amounts of ass. Right now it's basically up to user preference and what your budget is.
If I were you, I would get GTX 670 now that prices are starting to fall, and get another in a year for SLI.