Er, Bill, are you sure about that conductivity? Copper resistivity is less than 2 microhm-centimeter. (The lower the number the better the conductivity is one way to look at this.) Typical brass (a copper alloy) has a resistivity of about 7 microhm-centimeter. Steels typically range from a low of about 10+ (pure iron is 10) to over 70. The stainless steels tend to the higher end, IIRC - IOW, worse conducters than "ordinary" steels.
However - either will do for lighting off steel wool at 12vdc, I'm sure. Worst case, the resistance in the wire is higher than that in the steel wool and it gets red hot (even melts) and... FIRE!!! <grin>
But if you've got an automobile and juice in the battery, just use the cigarette lighter you tossed in the glove box - it gets plenty hot enough if you have tinder - try it out.
SS wire in an auto has lots of jerry-rigging potential anyway - I carry steel and copper wire in my vehicle kit, and you can guess which one is used for "structural" emergencies... Example: recently, one of my kids - new driver, clunker car - called to say that his right rear wheel had "fallen off" in the middle of the street. When I arrived, I found it pancaked, but still attached - the ball joint on the upper control arm was worn out and popped out. Jacked it up, squeezed it back together with a C-Clamp (those have been invaluable in the car kits over the years, too), lashed the ball joint together with steel wire, and took the clamp off. He drove it home several miles without incident. (And since then he has replaced ALL the ball joints and a bent radius arm all by himself, which tickles me.)
Drag out your CRC and see if I'm on-target about the resistance, but I think that I'm pretty close.
Be Prepared
Tom