I've got what I think your link (some pages back) calls a Gen 2 60GB PAL, or what most people would call a PS3 FAT. I don't see any problems with the XMB or stuttering in dealerships. I'm playing the game from disc. I have upgraded the hard drive which may help with heating problems. I've never cleaned my PS3 out so I wouldn't be surprised if it was full of dust.
The article linked to about the Cell chip speculates that it's got thermal throttling but we don't know for sure. Judging from what I've heard from it and from other peoples experiences, it just turns up the fan speed when it's hot and eventually cuts out if temperatures continue to rise.
I can say that the fan on my PS3 is noisier when playing some other games which would indicate that GT6 is not being throttled (if that is in fact possible).
Last edited: Dec 30, 2013