Stock IRAI is like shooting at a goal with no goalkeeper.
IRAI 41 will give you a challenge
IRAI 39 is less challenging but you will need the mod patch that goes with it.
Go to the Download Tab select SH5 go to the Patches Icon
You may have to look around to find both parts or try Google
Dwnload Link
IRAI_0_0_41_ByTheDarkWraith
http://www.subsim.com/radioroom/showthread.php?t=171973&highlight=irai_0_0_41