GTX 1050 Ti @ 900p should be enough for your gaming needs.
Here's a review of MSI GTX 1050 Ti Gaming X 4G GPU @ 1080p with FPS counts,
link:
http://www.tomshardware.com/reviews/nvidia-geforce-gtx-1050-ti,4787.html
In Battlefield 1 with medium quality @ 1080p, GPU got average of 79.7 FPS and min of 72 FPS.
In GTA V with high quality @ 1080p, GPU got average of 83.1 FPS and min of 62 FPS.
Forza Horizon 3 isn't covered in that review.
With solid 60+ FPS @ 1080p, you should easily get 60+ FPS @ 900p.
GPU purchase options as well,
pcpp:
https://pcpartpicker.com/product/H97CmG/msi-geforce-gtx-1050-ti-4gb-gaming-x-4g-video-card-gtx-1050-ti-gaming-x-4g
Though, with GTX 1060, you're looking high/ultra settings @ 1080p with solid 60+ FPS,
pcpp: https://pcpartpicker.com/products/compare/W9cMnQ,JVWrxr/
(In my Skylake build, i have MSI GTX 1060 Gaming X 3G GPU. Full specs in my sig.)