Preheat oven to 325°F. Grease a 9-inch springform pan and wrap the outside tightly with two layers of heavy-duty foil.
Pulse graham crackers in a food processor until fine crumbs form. Combine crumbs, sugar, and salt in a bowl, then stir in melted butter until mixture resembles wet sand.
Press the crust firmly into the bottom and about 1 inch up the sides of the prepared pan. Use a measuring cup to pack it tight.
Bake the crust for 10 minutes until set and lightly golden. Remove and let cool on the counter while keeping the oven on.
In a stand mixer fitted with the paddle attachment, beat softened cream cheese on medium speed for 2-3 minutes until completely smooth. Scrape down the bowl.
Add granulated sugar and beat until combined, about 1 minute. Add sour cream and mix on low speed until incorporated.
Add key lime zest, key lime juice, vanilla extract, and salt. Mix on low speed until evenly combined, being careful not to overmix.
Add eggs one at a time, mixing on low speed after each addition until just combined. Stop mixing as soon as the last egg disappears into the batter.
Pour the batter over the cooled crust and smooth the top with an offset spatula. Tap the pan gently on the counter to release air bubbles.
Place the pan on a baking sheet and bake at 325°F for 50-60 minutes. The cheesecake is done when the edges are set and the center has a slight jiggle.
Turn off the oven, crack the door open a few inches, and let the cheesecake sit in the cooling oven for 1 hour.
Remove the cheesecake from the oven and let it finish cooling on the counter to room temperature.
Cover the pan loosely with plastic wrap and refrigerate for at least 6 hours, or overnight for best results.
In a chilled mixing bowl, beat cold heavy whipping cream, powdered sugar, and vanilla extract on medium-high speed until stiff peaks form, about 2-3 minutes.
Run a thin knife around the edge of the pan before releasing the springform sides. Pipe or dollop whipped cream over the cheesecake and garnish with lime slices and zest.