Can't really give an exact answer. You'll just have to see how it goes. When I tried to keep two small silvers together they fought, I would seperate and try again in different tanks, with and without tankmates. No matter what I did these two aros fought, I finally had to sell one of them.
Later one I tired to mix the silver I kept with a black aro, it lasted for a couple hours before they started fighting. I was finally able to find a match when i adopted another large silver aro. I put the two together and they have never fought, it's been close to 2 years that they have been togehter.
I am planning on putting the two silvers and the black all together here in a couple months, I just hope all goes well.