That's ironic since it's the Bru'n water pale ale profile that had me targeting such high Ca levels!
The high calcium level is a by-product of wanting so much sulfate in the Pale Ale profile. Since you can't add sulfate without adding some other cation, we are going to end up with one of those cations (Ca, Mg, Na, K) high. Calcium just happens to be a rather innocuous ion, so letting its concentration rise is OK.
Calcium is really helpful in getting yeast to flocculate and it can help beers clear. But there is little reason to raise it above about 50 ppm for ales. The only reason to take it higher is to add those flavor ions (SO4 and Cl) to the water. In the case of the Pale Ale profile, it is a necessary thing.
However, this brings up another VERY important point about magnesium in brewing water. Mg is not a bad component in brewing water. In the case of creating a high sulfate content water like the Pale Ale profile, an Epsom Salt addition can really boost sulfate with a modest boost in Mg content (20 ppm Mg from Epsom provides 79 ppm SO4). That is a pretty good payoff in my opinion. In addition, the flavor from Mg is actually complementary to the overall bittering that we want in pale ales and IPAs. Including that Epsom Salt addition also reduces the total calcium that you will have to add if you are targeting a high sulfate content. This is a win-win in my view.
The Sulfate/Chloride ratio is purely informational and its only useful when the chloride content is at a modest level (say 25 to 125 ppm). Beyond those limits, the ions are either too low to really taste or too minerally for brewing.