The Asus P6T will work with the Xeon X5660.
The Asus P6T will work with the Xeon X5660.
Your ASUS P6T motherboard might work with the Xeon X5660, though Asus doesn’t list it in their supported CPUs. The manufacturer mentions it doesn’t support it, but some users have reported success. Please double-check compatibility before purchasing. Thank you!
Unfortunately I don't have enough knowledge about this to give you a reliable answer. But here are my thoughts from the post you linked it looks like someone has it working. Although there was no mention if the user had to do anything speshiel to get it working. But I would say there is a good chance it will work. The only different between the X5670 and X5660 is the speed so I don't see a reason why the X5660 won't work if a X5670 works. Supported CPUs are just CPUs that Asus has tested with the motherboard and have designed around. Basically it is a list of hardware that Asus garrentees will work with the motherboard. And It is you best chance of getting a working rock solid system. But just because it isn't on the list doesn't mean that it won't work.