Then I guess it's just me, but I'd certainly say that the burden of proof lied far more on the person who made a thread titled "GT6 framerate depends on which console you have" with specific claims related therein attempting to justify it rather than the people who say that it doesn't in response to when that first person failed to provide anything but anecdotal evidence (and various suppositions/statements of questionable veracity) to prove it does.
All things considered, the title is accurate. The thread has already elicited (and the OP has agreed) that there is not necessarily a concrete relationship between model and "performance"; but what is certain is that some people are clearly having a better time of it than others. It varies from console to console. The performance depends on which console you got, which seems to be true even amongst equivalent models.
However, you can guarantee that, all else being equal, a furred-up fatty (etc.) will run hotter than a furred-up 45 nm slim. The general expectation among those who know about chip design is that thermal throttling is present on the chip (as a simple extension to the load-dependent throttling that definitely is there), so the fatty will be closer to whatever limit is present (which may itself vary from model to model; but that doesn't change the outcome here). Add in variance from dodgy coolers, that from manufacturing variance (different voltages required to maintain stock clocks) and that from the specific environment, and the possibility space starts to make sense (even if we can't directly quantify any of it).
Some models will probably be running slow for different ultimate reasons (proximate cause likely to be "too hot"), and without servicing several thousand of them, we won't know for sure what the patterns are (Sony would have had an idea and integrated that knowledge into revisions, though - even on the "same model"). But, crucially, we don't need to know what the patterns are,
if performance drops are due to thermal throttling (it might be interesting to explore what else it could possibly be).
For now, if your PS3 is running badly, check the cooling - check the fans work, check you've got clear flow into and out of the console - and if possible
through the console, and make sure dust is nowhere to be seen.
@
xSNAKEx may benefit from editing the first post.
If there is contention with the basic idea that the game runs better or worse for different people, regardless of any notion of console (or display!) variability, that may be a long discussion.