I'll second
@JA600L 's suggestion to call them, but also add my two cents.
The top-end burn on the PH is definitely the highest output of the three stoves. The heat coming off the front during a strong secondaries burn is quite impressive; in our big, drafty farmhouse, we appreciate that power. My wife loves the heat still in the soapstone in the mornings (she feels the steel stove are quite a bit cooler by morning).
The IS is the biggest firebox, and has excellent air control. It is deeper front-to-back, which gives you some flexibility (you can load your splits in either direction - if I had an IS long-term I probably would cut my wood 18" and load N/S all the time). Loading E/W, you can pull the coals forward and put large splits at the back bottom to help get a longer burn. The IS has the most exterior surface area - at 400 degrees I assume it will be releasing more heat than the other two. It is a big stove - my wife liked running it, but felt it was too big for where we want our second stove. I personally don't like a front-loader.
The Absolute Steel is not small, but is smaller than the other two. It is simpler in construction, is a side-loader, and has great air control. We will be buying one as our second stove.
Probably your best bet is to see all three in person (road trip east?). A different company once gave me contact info for people living close to me who had a boiler I was interested in, and we did a couple of house visits. I don't know if Woodstock ever connects people that way, but it wouldn't hurt to ask.