Low fps in ubuntu 18.04 with nvidia card

Besides your graphics card and different Ubuntu version, my specs are all older than yours. Ubuntu runs much smoother for me than Windows 10. I think it be worth a shot to reinstall a fresh image and try what's below.

sudo apt-add-repository ppa:graphics-drivers/ppa

sudo apt update

sudo apt install nvidia-driver-390

Add nouveau.modeset=0 to GRUB to allow Ubuntu to boot up normally without affecting drivers.

In terminal, type

sudo nano /etc/default/grub

And replace the line that begins with GRUB_CMDLINE_LINUX_DEFAULT= to

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nouveau.modeset=0"

Hit CTRL+O to write it out, enter to save it, then CTRL+X to exit. Then update GRUB: sudo update-grub

If that still doesn't help you can try posting your syslog and maybe someone more experienced can help. I looked at mine and it turns out there was an issue with theh touchpad that's solvable.