1. The best dBm varies from device to device, however, I have never seen anything greater than -65dBm on an iPhone. (This is partly because I don't get around to too many towers, and I live in weaker signal areas.)
2. The iPhone won't tell you if you have eHRPD on your local towers due to the fact that the iPhone 4/4S lacks LTE.
3. 3G is EV-DO.
4. 1x shows what tower you are connected to as well as what frequency you are connected to as well. 1xEV-DO shows the frequency that you are connected to as well. They both show other things such as the tower identifiers like base station id. I don't have my friends iPhone in front of me right now to check the rest.