The contractor that I'll likely select will install whatever Manual J says for two stage, unless I decide on something different. In that case, he's willing to "fudge" the calculation to make me happy. He quoted me on the 4 ton XL20i, and after considering all I've read here, I've asked for a side-by-side quote on both the 3 ton and the 4 ton Xl20i so I'd know the difference in price BEFORE I make a commitment, and whichever one is installed is the price I'd pay. Discussed this with his "office" (actually, his wife) and she agreed that was a good idea. She promised to provide the updated quote.