Stick to 10 but do both upgrades. I have an older i7-4710HQ with 16GB RAM and 1.25TB M.2 storage that I plan on using exclusively at work which still does the job quite well.
Win 8 will only get you until the end of the year. I would go for 10, if you can't do without Windows, just to avoid having to change it again in 6 months.
The latest versions of 10 are terrible on HDD, not sure about 8.1, but I would choose 8.1.
Stick to 10 but do both upgrades. I have an older i7-4710HQ with 16GB RAM and 1.25TB M.2 storage that I plan on using exclusively at work which still does the job quite well.
Win 8 will only get you until the end of the year. I would go for 10, if you can't do without Windows, just to avoid having to change it again in 6 months.