I bought a new PSP-3000 last month and I believe it had firmware 6.31, when at the time the latest firmware was 6.37 or 6.38. I bought my 3000 from Walmart as they have by far the most lenient return policy and I knew if my PSP's firmware was unhackable I could just take it back with no hassles.
It doesn't matter right now what firmware it comes with. They have released downgraders for 6.38 and the newest 6.39. Therefore, it wouldn't matter if you cared about downgrading, homebrew, or illegal activities.
Seems like there is no clear answer. If it helps, two weeks ago I bought a "new" PSP 3000 at Target. It was on 6.37, so I returned it (of course, that doesn't matter now because of the 6.38/6.39 downgrader). Yesterday I bought a 3000 at another store, and it was 6.30. So go figure. I think 6.35+ is what you'll generally find.
Not true. Have had this also with a 3k that was on 6.37 but 6.35 was possible. That and i had a go on 6.20 that could also handle 5.70. Both came with the later version of firmware yet both downgradable..
Granted however there is a risk to any downgrading on the "un-hackables". However just dismissing something as not dooable is just silly.
All 1k in my experience can all go down to 1.00. Maybe the motherboard is the culpret here..... hmmm...
Came with out of the box? Retail UMDs will try to update the system before they play, so it's not uncommon to get a used PSP at a later firmware than it came with. Considering nobody's seen a Go come with anything lower than 5.70 I'm willing to bet that's your case.