Oh come on, Dave. Calcium is virtually tasteless, not chalky or metallic. Sulfate is not bitter at all. It is very drying though. Chloride does not have a salty taste. Its only when combined with sodium that its salty and that is only at levels much higher than typically used in brewing.
At the levels we typically use in brewing, any of those ions are only adding nuances to the flavor and pushing our perceptions of other beer flavors in one way or another. Don't worry too much about a perfect level of any of those ions.
In the case of Munich water, the sulfate and chloride are both naturally low. Around 20 ppm sulfate and 10 ppm chloride in the tap water. Of course, the brewers are free to add minerals to their water and there is no telling what they may be doing for a O'fest. I don't think they are adding much of anything, maybe some CaCl2 and possibly a teeny bit of gypsum.
Since O'fest is a lager, you don't have to target 50 ppm calcium. Lower is probably better. Something like the Amber Malty profile that is diluted a bit, should be fine.