All depends on what happened with the consoles during those couple of years and how far engine development went. It's still safe to say that 3 to 4 year about right sounds for medium settings with gaming desktops.
What I wrote in my previous post will get you that or close to. You'll most likely have a better PC or new laptop by than.
quick edit: that's talking about single-card systems. SLI/CF can and probably will last a bit longer on higher settings.
