The metallic will be shinier, and easier to see at night. Will shine off light and catch the eye better. I'd go with Metallic.

 

color is one of those things that you just have to look at hundreds of pics . narrow it down and stew on them for a few months. Then when your sure of the one you want you find out the price and pick whatevers close enough everybody is different. you know whats right for you. 911s look good in almost any color

 

I think Slate Grey Metallic is the best 911 color. My 997 had it. I had bought the car with 14k miles and it was an over $3,000 option.

 

Depends on whether you want it to pop or keep it stealth. Most stealth is a flat or matte grey, black is in between and the ones that pop are the blues/oranges.
Also depends on whether its a DD vs fun/weekend car. For DD, I would keep it stealth but if its a weekend car, go with something that pops.
For me, that would be the orange.
Good luck.

 

I would go w/ the slate grey!