EZ Water vs. Bru'n Water for dark beers

So, I've put the recipe I'm going to use for a Robust Porter (It's actually Jamil Z's.) in both EZ Water 2.0 and Bru'n Water 1.7 (This is the latest version as of a few days ago.). The SRM is about 37, estimated. My water is quite hard, with HCO3 at about 261 and calcium only at 87 (Magnesium 9). So, I obviously have a lot of residual alkalinity, just about perfect for this beer, I'd imagine. I plan to use 5 gallons of strike water for 15.5 pounds of grain.

When I enter in my water profile, Bru'n Water states that I need an SRM of 33 to cancel out my alkalinity. However, when I enter in the recipe on the mash alkalinity tab, I get the SRM estimate of 37, and a pH estimate of 5.4 when diluted by 15 percent with distilled water. I understand that the SRM to pH estimate isn't a perfect model by any means. However, it seems at least based on the water input tab, that my pH should be lower. EZ Water gives me a pH of about 5.1 without any dilution.

Theoretically I suppose Bru'n Water would be more accurate because I entered in the actual recipe, and I know Kai has found that crystal malts reduce alkalinity more per SRM than do roasted malts (The recipe has a pound of C40.).

Anyways, I'm wondering what people have found, which spreadsheet has produced better results for you, for darker beers?

The entire SRM thing has been removed from the latest version of Bru'n Water (v 1.9) since some brewers seem to be stuck on using it as a water adjustment criteria instead of the mash pH. The correlation between RA and SRM is pretty loose, especially as beer color gets into the brown and black range.

To get the mash pH to fall to 5.1 would take a large Net Mash Acidity and considering your water's RA of about 150, it is unlikely that it could fall that far. Are you sure your EZ Water entries are correct? I don't think it would predict that low.

I mash with water with a modest positive (my tap water) to modest negative (RO + some CaCl and maybe gypsum) RA and I only add alkalinity if I measure a mash pH lower than I want.

The lowest mash pH I ever measured was still a bit above 5.1 (a big baltic porter with a ton of toasted and caramel type malt). So 5.1 for a robust porter with fairly alkaline water doesn't jive. I would guess Bru'n water is closer on this one.