Is a louder IC cable a better cable?

This may sound like a weird question but, from what I've been reading about IC cables, they can't really add anything but they can "get in the way". Assuming that's the case, would the fact that one cable plays louder than another mean the quieter cable is "more in the way"?
I'm demoing 2 cables. one is an RCA and the other XLR, one used with a retail of close to $7K, one new retailing for $2.5K.
I know the common answer is "Go with what sounds better" but here's the hitch. If the idea that louder means there's less in the way, it would also seem to mean that you're hearing more of what's really there, and that's a truer sound, so if something doesn't sound right beyond that point you can look elsewhere in the system. At this point it is very difficult to navigate the cable market because I know for myself that I don't know how to make an educated decision. The "listen and choose" method is the best most of us can do for now but in a way it's ignorant and childish.
I think a good way to "test" cables would be to run let's say 100 frequencies between 20Hz-20kHz and see how "purely" the cable transferred each given frequency. Maybe this is how they design cables now, but the industry is so shrouded in hype and non-disclosure that it all is a bit of a mystery. Any isight will be appreciated.
Almost always a XLR connection will have more gain than a RCA
connection. That's how a truly balanced connection works.

I'm assuming the XLR cable is "louder" than the RCA cable?
Mofi is of course correct. When you change between RCA and XLR you are not only changing the cable, you are changing between different interface circuit designs in both of the components that are being connected, and you are changing between kinds of connections that operate on different principles.

Often, although not always (depending on the specific component designs), XLR connections will result in 6 db greater volume than RCA connections between the same components.
I think a good way to "test" cables would be to run let's say 100 frequencies between 20Hz-20kHz and see how "purely" the cable transferred each given frequency.
I doubt that would be likely to prove anything. Partly because music signals are much more complex than the simple sine waves each of those frequencies would consist of; partly because the sonic effects of a cable can be expected to vary significantly depending on the technical characteristics of the components the cable is connecting (a point that seems to be under-recognized by many audiophiles, IMO); and partly because there would be no consensus on what parameters should be measured to assess the "purity" of the transfer.

-- Al
An XLR cable is not louder than an RCA cable. The balanced output feeding the XLR cable typically has more gain.

So, no, don't simply choose the louder cable because one cable isn't actually louder than another. However, with some gear it's truly beneficial to run balanced connections.

For instance, in my system my phono preamp has RCA and balanced outputs. The RCAs are the better outputs, even though the output via the XLR would be 6 dB louder.
All other things being equal, a longer set of speaker cables will have more resistance which means slightly less volume. Does this mean that the shorter cable is better? No, it simply means that shorter is better.

There are so many potential factors in different cable designs and the parameters that could lead to volume differences are only a piece of the overall puzzle. RCA to XLR is apples to oranges as other have said.
No offense, but if, as you said, "I don't know how to make an educated decision", you should not be spending thousands on cable until you do. That could come by way of your own experience or employing the help of someone you trust. IMO, you should purchase some decent, reasonably priced cables like Audience or some other brands and listen to them for a year until you build up a point of reference. Listen to every record you own until you know what everything sounds like. Then, when you have it figured out, you can substitute an expensive cable like a Stealth or whatever and see if it truly improves your system over what you already have. At least that's what I think.
Thanks for the feedback. The XLR's are of course the louder cable and that being factored in they, to my ear, still sounded worse in my system/set up; back they go.

The point I was making about making an educated decision was addressing the difficulty in finding out more on the science of metallurgy on sonics. I realize that beyond the science there's a multitude of other variables but at least it's some place to start. It's all well and good to "just pick what sounds best", but without a reference based in some sort of scientific reality, there's no foundation for rational assessment.

For example, sonics are a combination of art and science, creating sound waves in real time. Visual art forms, which are sometimes created with science, are usually static and are generally assessed on aesthetics. Even in visual art there is study and education that helps an educated viewer or buyer to understand the value of a piece based on it's relevance, whether it's truly original or derivative etc. besides just deciding that you "like it". So I figure the more we know about the "how's" and "why's" the better. There is so much big talk about cables, and as anyone with a system that's resolving enough to hear the difference, it's totally obvious that they make a huge difference. Sorting through the hype and trying to justify the costs is a whole other issue. That being said there's probably more hype and b.s. in the art world then in audio since there's so much more money in it, but there you go.

Also, I do have some pretty decent, at least to my ear, cables and am living with them. I almost always buy used here on Agon so experimenting is an option since a decent used cable can usually be sold for close to it purchase cost if it doesn't work out. I'm in no big rush to change for changes sake. However, besides loving music I enjoy the audio gear hobby, hearing how different things sound and working towards a system that keeps sounding better and better.

So far it's working out pretty well and I really appreciate the opportunity to interact with others that share the appreciation of the hobby and their love of music.