Question ROG STRIX Z390-E GAMING

MicroXBox93

Distinguished
Oct 27, 2012
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18,515
Hi all!
Quick question, bought the above mobo recently haven’t received it yet, before making another move like purchasing 2 - m.2 of 1tb each, is it a good idea using both slots and avoiding using the standard speeds of an regular ssd (sata)?

Im planning on 1tb m.2 for Windows and programs, 1tb for games movies and such,
I’ve heard that on this specific motherboard - ROG STRIX Z390-E GAMING:
Using both slots will decrease pcie speeds to 8x or am I wrong ?
Appreciate if someone would explain better
Thank you !!

my rig -
I9 9900k with NZXT kraken x6
Asus ROG strix z390 Gaming - E
16gb ram , 8x2 2666 (will change to 3200)
1070ti Zotac - will change to 2070 super