quite franky, you can't trust either mbm or sandra. MBM4 is probably giving the right reading, but that mb uses a thermistor underneath the socket to measure CPU temp. Even though many people think this is accurate, it is highly inaccurate. Even if the thermistor is touching the bottom of the cpu, all it is touching is substrate.
With k6-2s and older socket cpu's, the hottest part of the chip was underneath. Back then, a thermistor solution was a bit more accurate. Nowadays, with flip chip processes, the hottest part of the cpu touches the heatsink. The backside is fairly cool substrate and some resistors.
IN playing around between a 7vca and a cusl2(which supports on-cpu diode temp readings), i get anywhere from 10C to 15C higher than the 7vca with the cusl2. Expect your cpu to be running anywhere from 45-50C with the 7vca, even though mbm won't report it. YOu can compensate for this, but it won't show sharp cpu temp changes.
Mike