To be honest, I build systems that stand the test of time for at least two years. At the moment, no PC game has "rocked" my system because it just doesn't exist (yet), even though the GFX Cards (plural...2) are 8 months old, and the CPU is 12 months old. The Dual-card setup is working amazingly. Alone, a single card probably could be killed by all the HD Patches I put on Skyrim, but together, the cards are working in tandem which mean my framerate with all HD at Maximum on Skyrim is operating at 76 FPS inside, 49 FPS outside in full view.
When I hit the "limits" of my system, I start researching for a new setup. I find the weakest link (slow RAM, slow CPU, slow GPU) and aim to replace only that component (unless old components are incompatible with new components). If I find that the computer is still underperforming, I perform further upgrades.