Slot 1 runs hotter than Socket 370
Based on the info you have, you cannot say that. Two different mobos about which you know little re- their temp measurement functions. All you can say is that they give different temp readings. That by itself tells you little about the CPU core temp especially as slockets also have their own idiocyncracies.
Many earlier slot-1 boards did not read the diode and used a thermistor sticking up next to the slot meant to make contact with the edge of the CPU core when it is plugged it, Thgey did not work very well. Asus is also known to compensate for thermistor inaccuracies by adding 10-15C to the actual reading.
So, there is little you know about slot 1 vs Slot 370 on the basis of your info. I would consider your 370 temp reading more accurate but also question whether the setup in your slot 1 boared was correct. It is the same CPU, there is no reason it would work at SUCH different temps.