Negative 17 80mm stem on MTB?
Lowering the hand position will essentially move your shoulders forward and down, in an arc.  This will put your head further forward, and you'll have to look up slightly more.  It will also put more weight on your hands.
If you currently ride with your elbows slightly bent, then they will end up straighter.
This will also very slightly rotate your pelvis forward too.
I'd suggest confirming your saddle height is good first - assuming you're riding on the road, then it should be high as possible but not enough to make your hips rock side to side.  If that happens, lower it by a few mm.
Also if you're riding on road only, you don't need the wider handlebars.  Narrower bars let you fit through traffic gaps better, and will be slightly more aero.