I would load 8 rounds and not worry about it. You probably won't ever need new mag springs. I have never believed any spring should be used fully compressed. The wire stacks on itself and it's a one-way spring. The cartridge pick-up rail puts additional pressure, on that spring, when you shove it into your gun.
I believe, I'm the only Glock owner that thinks most all Glock magazines should be down-loaded by 1 or 2 rounds, depending on the caliber.
The contract, to supply the Austrian army the G17, required only 1 mag to be furnished, if the pistol held 16 rounds or more. Glock saved a tidy sum, in just mags. He wasn't a gun engineer, he just wanted to cram the most ammo in a reasonable sized magazine.