Found this on a site for 360 achievements..and so far this is all I have been able to find in regards to Trophies/Achievments:
Rocksmith achievement/trophy video guide at quick360achievements.com | quick 360 achievements
My guess is 5g is bronze, 20G - Silver, 40G - Gold. They seem pretty straight forward. Tho its kinda confusing with 5G, 10G etc haha. I don't play 360 or own one..so if someone wants to help translate ..by all means. When I find an actual trophy list I will update this!