In my experience, the main difference between any SF and his respective NF is that the SF wants to be nice to people; the NF wants to be Good (as in against Evil!) For the NF it's a broader struggle involving a lot more than just himself and the people in that particular scenario.
A friend and I were discussing The Brothers Karamazov and trying to decide between SFP and NFP for Aloyosha. We decided on NFP, largely due to one scene where his obnoxious ESTP father spits on a cross, and Aloyosha breaks down, drops to the floor and starts bawling.
This is very telling because the SFP response here would be smaller in scope: "Hey, that's pretty mean!" It's mean because if somebody religious sees it, it might hurt his feelings!
The NFP sees the broader implications of the spitting on the cross in context, and the hateful attitude it shows in his father is enough to really hurt him. NFs are less capable of dealing with all the evil and injustice in the world--it plagues them constantly. The SF doesn't approve of such deeds any more than the NF, but finds it easier to ignore them when they aren't happening in his particular physical environment. On to the next present-moment distraction!
Both are drawn to helping people, but the NF wants to do this in a grand, broad-sweeping way. I might have mentioned this somewhere on this board before, but it's a good example of SF vs. NF so I'll restate:
An NF friend of mine had a brother who was arrested for marijuana distribution. "I just wish I could do something to change marijuana laws!" she lamented. She wants to make a broad idealistic change that will prevent this kind of perceived injustice from happening not only to her brother, but to anyone ever again! That's really NF.
The SF here is more likely to look for practical, physical task-oriented ways to increase his level of immediate comfort while he's in jail. "Let's bring him some hot soup and pillows and blankets!" is a more likely SF response.