My guess is they're about the same performance. I don't know precisely, since my only experience with AMD APU integrated graphics was the A6-5400k.
What I can say, though, is that with the GTX480 (almost misread that as an RX480 for 25 bucks, almost got slightly triggered), you'll be reducing the load on the APU as a whole, as well as not having to share RAM, heat dissipation, and power, so the CPU part of the APU can finally run as fast as it wants, and the GPU finally has its own entity, so the two components no longer hinder each other based on physical demands. Also, your APU will run a fair bit cooler since half of it isn't even on anymore. In general, even if the GTX480 and the integrated graphics are the same performance-wise, your overall performance will go up. This certainly was the case when I finally bothered to pair my POS R7 240 with my A6-5400k.
In fact, I'd hazard a guess that your system would become fairly balanced, without much of a bottleneck on either end. Of course, that depends on the games you're playing. BF1 is a very different beast from Tomb Raider.