In answer to both the questions, firstly, not sure what I am going to do with this set up yet, as the next set up is a 10x2.5x2.5, and will take pride of place in the new room at the house. This set up is only a year old, and is a 7x2x2. I should have ordered the bigger set up straight away!
As to aggression, they have only gone in together first time today. So far they seem to be happily swimmimg around, they haven't shown any aggression yet, but we haven't had a feeding time!!!
The silver has always been very laid back, and the green came from a smaller tank, with small tank mates, so I guess we will have to wait and see.
Thanks for comments.