You are buying a card to max out settings and keep your rig relevant for the next few years, so we want you to choose something that won't need an upgrade next season. A good high-end GPU handles heavy rendering and fast motion smoothly, saving you from buying twice.
Wait for the next chip architecture to drop before you buy. When newer models hit the market, stores usually mark down last year's top-tier cards, and that overlap is where you get the best performance for your actual dollars.
That 18-month window is a hard deadline, not free money, so any balance left when it ends will start racking up standard interest.