I hate to be a total idiot here but I'm going to wade in anyway.
What is the difference between simply targeting a mash pH of 5.4 (by not adding ingredients that will force it lower), and adding Baking Soda or Pickling Lime?
I'm really trying hard to get this, but it sounds like a math problem that goes like this:
The answer is 5.4. Assuming I start with 7, I can get there this way 7 - 1.6 = 5.4. But I hear it being said that I need to get there by doing this: 7 - 2.3 + 1.3 = 5.4. (with the 2.3 being a made-up number - the point being that it overshoots the 5.4 target)
So I ask again: is the primary thing the resulting pH, or adding Alkalinity? Another way to ask this is, is there something being added beyond the manipulation of pH when one adds Baking Soda or Pickling Lime? I hope I'm not ticking someone off here with my denseness, but I honestly feel like I'm being ushered into a round room and being asked to sit in the corner.
No idiot questions here, especially when it comes to water. In the end, what you're looking for from water are a) pH and B) concentration of flavor ions. It doesn't make much of a difference how you get there. Alkalinity is part of whet gets you to your pH, but it is NOT your end goal.
Basically, you have your starting water, your salt/acid additions, and your grain bill. These all factor in to determine your pH. So when you ask how much lime you add to a 5-gallon batch, the only correct answer is "it depends". I'm assuming that when Martin said he needs to add lime to his Pale Ales, it's because with the mineral additions he uses (including ~300ppm of Sulfate from gypsum/epsom salt) and his grain bill, his mash pH would be too low if he didn't add lime. Your water and grain bill may require a different amount.