From what I understand, the MAP advance curve is basically what the old vacuum advance canisters used to do on the side of old distributors. What they were set at varies car to car, but on my 5.7 at least I tend to idle right around 6 psi or so (which is right around the point where the stock curve starts to drop off). On the old canisters, as the throttle opened, the vacuum advance would drop out, which is what the curve does (higher psi means lower vaccuum since it's measuring absolute pressure where 14.7 or so is atmospheric). So the MAP curve is basically a parallel to the old vaccuum advance curves.
The rpm timing curve is effectively your mechanical advance. As the engine speed goes up the timing goes up. This was done with weights in the distributors on the old cars, but it's the same idea on the cuve.
MSD claims the stock curves are good for premium fuel on a stock engine (American premium around 91-93 octane at least), but I've run on 87 with no issues so far. It seems like most people running a carb setup have good luck bumping up the mechanical curve across the board. On mine I've added 3 degrees of timing at each point (except for the left-most idle point and I took out the little cut on the end of the curve and have had pretty good luck. It seems to like the extra timing and so far I haven't heard any horrible noises. I'm still even running it on 87 octane, but it's just a base 5.7 with the Indy intake and headers, no internal work done. I can try to get a picture of my graph up later if you'd like. Not sure what the 6.1 likes for timing though, would have to ask around on that one.
