You are buying this rig so you can play current games without stuttering, and if you pick the right bundle, it should easily last you through the next console generation. Aim to buy once and keep it for years rather than chasing every minor hardware refresh.
We always look for holiday bundle deals because that is when retailers actually throw in extra controllers or game libraries for the base price. If a brand new version just dropped, look closely at last year's model instead, since you usually get 90 percent of the performance for a lot less cash.
The intro window is a deadline, not free money. If you still carry a balance when those 18 months run out, you will get hit with back interest on the whole amount.