You don't NEED a s/s battery in a s/s car. The OE battery in my Fiat was an s/s type, massive and very heavy, but only 64Ah capacity.
The break down guy replaced it under warranty with a standard battery - same physical size/ weight, but around 120Ah capacity.
I've been running that way for a couple of years and it works fine. Makes me wonder if s/s batteries are a con. Running a battery that you normally find cranking a V8 in a sub 1 litre car should mean a long life.
If you rarely stop, there's really no reason to run an S/S battery. You could run a much smaller conventional battery (possibly at a shorter life), or a big conventional battery (S/S still works on my car).
The economy gains from LiFe come primarily from their improved charge efficiency. If I took my Pb battery car, mains charged it to float then drove around the block, it would take around 20mins of mains charging to bring it back to float (essentially ~3Ah of capacity vanished on every start). That's why normally I'd charge it once a week and it would take up to 2 hours (~14Ah) to come to float.
With the LiFe, the battery is always 100% charged. No need for mains charging at all (charger shuts off immediately when connected). No charging losses as it approaches full, unlike Pb. I got a decent gain in low end power from the alt noticeably having less work to do.
Even on a cold start, because the alternator keeps the battery 100% full, the battery won't really be receiving a charge to speak of.
A second of cranking only takes about 0.2Wh out of your battery. Your car should also start much faster on LiFe. My LiFe maintains nearly 13v while cranking, even a healthy Pb sags to 12v or less.
Cold charging is a problem for EV's and alt deletes and the like charging from a low SOC. Any charge from a near full SOC shouldn't present a problem.