A GTX 960 will easily run with that system config and power supply (with no overclocking). The Antec VP450 has two 12V rails with 18A a piece and a maximum of 360W combined on the 12V rails. A standard GTX 960 requires only a third of the wattage on the 12V rail (120W); the processor another third (rated at 125W). If you're not overclocking anything or only applying a slight overclock (OC), you should be just fine. Introducing any OC is hit or miss though. If you don't OC. you're all set.
I have a GTX 960 with an i3-2100 in an HTPC I just built for my man cave. Even with the weaker older 3.1GHz dual-core processor, it blows any "next-gen" game console away.