Originally Posted by playerkp420
Yes. I have a cech-2501a and it came new with 3.40. Also I have downgraded 2 cech-2501b. Which 1 came with 3.40 and the other 3.50.
I believe the models that started coming with 3.56+, are cech-2504a and 2504b.
That chart on ps3devwiki is a little hard to read, because it does not show all the numbers. But the best way to tell for sure is the minimum firmware pup.
The last 2 numbers only determine the region. The letter also determines the HDD size.
2501 = USA, 2504 = Europe. A = 120/160GB, B = 250/320GB.
There is no way to make the difference between downgradeable 25xx and undowngradeable one, apart from looking at the date code at the bottom of the PS3, or using the MinVerChk PUP.
Note that the PS3DevWiki lists 250x and 251x separately, however this is irrelevant, I believe it was said it's because the 160/320gb model was released at a later date in Mexico (region 11) and Hong Kong (region 12). 25xx is 25xx, as I said above, the last two numbers only determine the region.
PS3 Slim CECH-3004A 160GB (500GB)
PS2 Slim SCPH-70004 - FMCB 1.8b