MSI B450 Gaming Pro Carbon AC MB M.2 Slot Question

Hello, i recently bought MSI B450 Gaming Pro Carbon AC Motherboard, Ryzen 2700, 16GB Corsair Ram. Will use old video card and Power Supply

i would like to use both M.2 Slots, 1 slot for window, 1 slot for gaming, however i didn't realize Slot #1 is 3x4 speed and Slot #2 is 2x4 speed.
i already bought XPG Gammix S11 Pro 512GB NVme M.2 and Samsung 860 500GB SSD, now i'm shopping for 2nd M.2 Drive (WD Black SN750 500GB or SN500 500GB)

which drive should i use it for windows and gaming?

Option 1
M.2 Slot 1 3x4 will be XPG Gammix S11 Pro 512GB (Gaming)
M.2 Slot 2 2x4 will be WD SN500 500GB (Windows)

Option 2
M.2 Slot 1 3x4 will be XPG Gammix S11 Pro 512GB (Windows)
M.2 Slot 2 2x4 will be WD SN500 500GB (Gaming)

thanks