I didn't know there were golden guns in the game, but I'm almost glad I didn't.
Golden guns look really tacky.

The big thing about the golden guns is that on subsequent play throughs, they are available from the very beginning of the game. Being able to get the Inertial Element, the game's best weapon, right at the start makes things a lot easier.
 
In terms of functionality though, they are exactly the same as their non-gilded counterparts.

From what I've read, they give out more XP when used, but I could be wrong.

I just know that you need them to do some speed runs since you can avoid getting the pistol at the start.

Yes I believe that there is no advantage beyond sequence breaking and having them from the start

" st glad I didn't. Golden guns look really tacky. "

" @FlamingHobo said:

" st glad I didn't. Golden guns look really tacky. "

Couldn't agree more with that. "

Well, as far as I'm aware they don't take up any % of items. So you can use the Inertial Element from the start and still do the game with 4% of items.

They give youe twice the Xp as normal guns.

Golden guns are badass....for a little while. I haven't gotten all the gold bars yet so I have yet to play with them but it definitely is not a necessity. Still, you can get them from the get-go so the game is easier in the long run.