I started pushing my water spreadsheet before I went on my brewing hiatus and haven't picked up that effort. After all the question is not so much the RA that is calculated by the spreadsheet but it is "can you brew better beer with a more accurate spreadsheet". John does recommend to limit the RA to 250 ppm and there is also a lot of leeway when it comes to the correct RA for a given beer. In addition to that he also doesn't account for mash thickness.Maybe Martin and other brewer's interest motivates me to write the next version of my water spreadsheet which will take more grist information into account. I do have a lot of the data necessary for that. Ideally this work should be incorporated into a commonly used tool like BeerSmith.
I also think that you can add all your salts to the mash and don't add any to the sparge water.
I'd love to have a Grand Unified Theory of Brew Salt Additions hammered out that takes mash thickness, temperature, grist composition and accurately predicts pH, RA, and so forth. I'd love to see it incorporated into BeerSmith along with better instructions for data entry as well as for brewing (e.g., Kai's recommendation to add all the salts directly to the mash, not the HLT or the Sparge Water).
Martin, thank you for looking into it, as well. Everytime you post something about water chemistry, believe me, I pay attention. Your expertise is evident--it takes me a few reads and re-reads to "get it.") Thanks for your input. Perhaps a collaboration with you, Kai, and A.J. and any others who are interested (e.g., those who design and run BeerSmith) is in order.