Forza Motorsport 6: Apex has had its official PC requirements released, with Turn 10 Studios' driving game requiring some relatively modest PC hardware to play the game.
You'll need a decent dual-core CPU with 8GB of RAM and an NVIDIA GeForce GT 740 or AMD Radeon R7 250X video card. If you want to hit 1080p 60FPS, you'll need a GeForce GTX 970 or Radeon R9 290X. 4K 60FPS isn't too far away, as you'll need a GeForce GTX 980 Ti or Radeon R9 Fury X.
Other than that, Turn 10 recommends an SSD + 30GB of HDD space for 4K 60FPS gaming, while you'll need 6GB or more of VRAM for 4K 60FPS. Turn 10 suggests an Xbox One controller for your input, which is going to be much, much better than playing Forza Motorsport 6: Apex on your keyboard.