IMO gun safes are a case where the law of diminishing returns comes in. I've seen a case reported by an owner where a cheap Sentry Centurian that was bolted down stopped a 'smash and grab' type of attacker. I have also seen a TL15 rated safe that was cut open by the owner's tools.
A high quality RSC (a useless rating) can stop some pretty aggressive attacks with non-power tools (I.e., pry bars, sledge hammer etc.) A tool rated safe will certainly stop any attack that a lower rated gun safe can but it may or may not stop an attack involving power tools. So you can spend 5 times as much for a safe that weighs 5 times an RSC and still be volunerable.
I agree with gearhounds and diablo that concealment is the best defense against an attack. Best example I've seen is where a friend of mine created a vault under the concrete frost wall entry way to his house. He cut an access door to it from within his basement then hid it behind a tool cabinet that was on casters so he could move it out of the way when needed. The only person who knew it was there was his wife and the only reason I found out about it was because I helped him move.
...probably the greatest concentration of talent and genius in the white house except for perhaps those times when Thomas Jefferson ate alone.
John F. Kennedy, Describing a dinner for Nobel Prize winners, 1962