It will be an interesting case if it goes to court.
Gold4RS should just avoid it and change their name imo.
There are two different ways to look at this:
1. Gold4RS can use the name Runescape because they are demonstrating compatibility. For example, if someone made a program called "Reader for Windows 7" it should be legal as it implies the product, as in reader/gold, being compatibile with a service, runescape/windows 7.
2. Gold4RS cannot use the name as gold for runescape sounds like it implies they are affiliated with jagex. Perhaps gold4rs would need to place a disclaimer on their front page or have a generalized landing page if they wanted to continue using their original domain.