Recommended specs according to Steam:
Intel I7-3770 / 8 GB / GTX 1060
Please keep in mind that Mafia 3 is not optimized; not even close. GTX 1060 will achieve average 50 FPS (1440p) and GTX 1080 will achieve average 60 FPS (1440p).
Joker Productions: Mafia 3 PC Performance | RX 480 vs GTX 1060 & 1080
https://www.youtube.com/watch?v=xvwidWDkI7s
By the way, if it's in the budget, I recommend upgrading RAM to 16 GB (8 GB x 2 kit) as a lot of games are recommending that much now. With the i7 processor, you'll need to also purchase a CPU cooler, as overclockable Intel processors don't come with one.