70° C is a little warm.
Have you tested the probes together (in a plastic bag in water for example) and checked that they read the same?
I used to measure CPU temp this way, on the Tbirds, and your numbers are a bit too high. You would definitely want to get them lower if you want to overclock.
I used to thead thin wires under the actual socket, not between the CPU and socket. You are running the risk of tilting the CPU and thereby causing a bad contact with the heatsink. I am guessing that this is happening. If that is not possible, cut a groove in the top of the socket, a channel for the thermistor wires. Void your warrantee.
