The numbers used are probably wrong, but it should get the point across.
I wanted to reuse my stock S939 HSF that came with my 3500+ if/when I bought an OEM 3800x2. The problem is my 3500+ was a 65W chip, while the x2s were 89W or higher. The sink just can't handle that much heat. I'm doing the same thing but reversed righti now. I'm using a stock quad core heatsink on my E6t600. The 6600 is an 65W chip, but I'm using a stock sink thats designed to handle more heat. As long as the stock sink can handle the heat, you should be good to go. Just look up the heat output for the chip you have, and the chip you hope to unlock it to.