I'm not sure what my actual furnace savings are because I also did a big insulation upgrade at the same time. I can tell you that my heating bills are about 50% lower than previous years but I was replacing the original 50 year old furnace that was maybe 65% efficient.
For me it made perfect sense just because government grants covered a fair bit of my cost, 25% for the furnace and 90% of the insulation. Lennox also rebated a few hundred bucks on top of that as well.
I don't recall what the price was for the one model up "signature series" but obviously the price and/or features didn't impress me to move up from the elite. Plus for only a few more percent in efficiency it likely wouldn't pay itself off.
The S is a good amount more efficient, my earlier point being the actual combustion efficiency number isn't as important as the companies want you to think, how the system works will save you real percents, we are talking 30% for a properly done delta t/ outdoor reset system {hydronic with storage}... Modulation and temp control via the outdoor temperature is where you save money...
Think of it this way, your biggest foe is being oversized, nothing waste more energy than an oversized flame. Your burner is sized to heat your home to 70 degrees on your design day temperature, around here that is 0 degrees, which makes up for a very small percentage of the heating season {OK not this year, but every other one, lol}. So this means you are over sized and running inefficient for most of the season... To get around this you modulate your burner so what happens is when it is 50 degrees outside and you only need 22K BTU to satisfy your heat loss, that is all the burner fires, as it gets colder the fire rate rises in small increments {thats full modulation} This save heaps of energy, but is a little tricky to make work in a furnace since it is only heating air, boilers with water as a buffer are much easier, so instead of full modulation the do stages, and your elite is a high low furnace {they have had this technology for years, first one was the carrier 2 stage, you controlled with the t-stat, then they switched to a timer, now its much better}.
That being said, the S modulates in 1% increments, so it is as close to full modulation as you can get and when they couple it with the variable speed blower, and their inducer variable suction system {this is where the others really fall behind, even in the low stage your furnace is still sucking the same amount of air out of the heat exchanger and depositing it outside your home as if it were in high fire, where the s modulates this according to the burner level} you get a really good amount of savings... also I have never heard a guieter funace than the S series...
They don't show huge savings in a chart, but that is actually becuase they show the s savings for all of the he lines, not sure why, but they do... Ill bet the s saves over 10% over the E's, and the early E series used to not come with the ss secondary heat exchanger, they now do but it took a while...
All of them are very nice units, I prefer armstrong air and that new carrier unit is sexy {we have done a few of them}, but you pay for it that is for sure, and nothing is as quiet as the S series, the armstrong is close, but that S is almost silent, it even ramps up the fan so you dont get the bang and forced air...
anyway, Ill stop here, since I can talk about this stuff for ever, Its a larger part of my life than it should be, sad to say..
