I have an 2007 mini intel core duo 1.83 ghz, 1gb memory, running 10.6.8 snow leopard. I can't find my discs and I need garage band. I can upgrade to Lion for $19.99. I need 2gb minimum. Should I upgrade with 2gb or 4gb? I understand that with 4gb, the mini will only access 3gb. That extra memory 1gb worth it?