There is no reason you cannot dose tanks that large, although a calcium reactor may be easier as you said, but I also prefer dosing as well. Buy the ingredients in bulk from bulkreefsupply during a group buy. The cost to dose a large tank is nowhere near as expensive as some claim. The table of costs that alot of people post is done assumin you were buying one gallons worth at a time. They have free shipping at BRS so it is even cheaper.
Mis up a bunch at once, I would store it in 5 gallon jugs or larger so you have to mix less. Recipe 1 may be easier to dose, since you need half the amount, so the doser will run that much less. If you find samller dosers like the drews dosers not keeping up, you cna always go to a litermeter or higher volume doser.
I have dosed on a 175 SPS tank with 55 gallon sump, and i had zero trouble with it.
