Hope this helps - I am basing this on our analysis software standard library data and I have not verified against any original ITE data, but I believe this data to be correct. Usual disclaimers apply. If anything doesn't look right, let me know.
Test Basis for both is ANSI-Symmetrical current basis.
5-AK-250:
MVA = 250 MVA
Nom kV = 4.16 kV
Max kV = 4.76 kV
K Fact = 1.24
Close & Latch = 58 kA
Interrupting Amps at Max kV = 30.3 kA
Max Interrupting Amps = 51 kA
Interrupting Time = 5 Cycles
5-AK-350:
MVA = 350 MVA
Nom kV = 4.16 kV
Max kV = 4.76 kV
K Fact = 1.2
Close & Latch = 78 kA
Interrupting Amps at Max kV = 42.5 kA
Max Interrupting Amps = 37.5 kA
Interrupting Time = 5 Cycles