I couldn´t tell for sure.
What I can tell is something I found in other forums, although I couldn´t tell how reliable because I never had to check it:
HOW TO DETERMINE THE FIRMWARE OUT OF THE BOX
===================================[Last updated on July 8, 2006]
no letter = 1.0 (
Japanese Release)
1.5 (
North-American release) confirmed
A = 1.5 confirmed
B = 1.51 confirmed
C = 1.52 confirmed
D = 1.52 confirmed
E = 1.52 confirmed
F = 2.0 confirmed
G = 2.01 confirmed
H = 2.50 confirmed
I = 2.60 confirmed
K = 2.71 confirmed
L = 2.81 confirmed
M = 3.01 confirmed
N = 3.03 unconfirmed
O = 3.10 unconfirmed
P = 3.11 confirmed
R = 3.40 confirmed
HOW TO DETERMINE A TA-082+ OUT OF THE BOX
================================
The pictures says it all:
"WS259" means the psp has a
TA-079 or TA-081 Motherboard. (Old type motherboards)
"SS259" means the psp has a
TA-082 or TA-086 Motherboard. (Newer type motherboards)
Both are downgradable as long as they are 3.50 or lower.
====================
I hope this helps

EDIT: Fanjita, you beat me posting
