you can use Trucha signer to know which IOS is needed to run a game.
Go to partition 1 GAME (not 0, RELSAB is the update partition)
and click on tmd.bin
look at the System version line, the 2 ending numbers are the IOS in hex format.
Ex.
Muramasa US :
Partition (RSFE7U)
clic on: tmd.bin
look : system version: 0000000100000035
35 in hexadecimal = 53 decimal
(you can use windows calculator in scientific mode to convert hex->dec)
the game will run on IOS53
some values :
hex | Dec (IOS)
23 | IOS35
24 | IOS36
26 | IOS38
37 | IOS55 (Metroid prime Trilogy PAL)
3A | IOS58