So the people on that forum said that if you disable hyperthreading Maya renders faster?

Well that is not unexpected. Hyperthreading is just tricking the system into believing that it has two cores, the CPU doesn't actually have two cores, so its behaviour is not like a mutlicore or multiprocessor at all.

I remember when hyperthreading came out a few years ago, there were all these article in magazines saying they slowed down certain types of apps.

As for the link, well I think you forgot or am I supposed to search the forum myself?