CPU heat

The quad, since most run at a higher wattage. But the stock heatsink is adequate, or better ones, such as the hyper 212, run about $30.

You need to look up the specific wattage of the processors in question. There were some Pentium 4 single core processors that took way more power than some of today's fastest quad core or even 6 core processors of today. But as a general rule of thumb, the more cores in a processor the more wattage it will use compared to a smaller processor of the same generation.

I was referring to Intel's QuadCore i5-760@2.80GHz w/ 95W MaxTDP & Core2Duo E-7500@2.93GHz w/ 65W MaxTDP. So how much heat do you think will a quadcore cpu generate compared to a dual core cpu?

The i5 runs much warmer. The recommended tdp by Intel is 72.6C. 40-70c is ok.

How much warmer? Is there a mathematical equation to measure the heat difference generated from each of theses cpu's? Or a simple experiment or test?

You running an experiment? Or writing a paper for class? Google it for test results.

Unless I am mistaken, heat should pretty much track wattage pretty closely with 65w making less heat than 95w and both making less heat than 125w.

You can get 125w to run cooler than the average 65w with a good cooling setup, but with the same cooling for each of the 3 (say, Hyper 212) they should have temps roughly according to wattages.