There aren't many people who have gone through both so I don't know that you will get a good comparison from one person. However, maybe you will get some input from Marines and from soldiers so that you can compare them.
I was an electronics technician, so I went to Infantry Training Battalion rather than SOI. We fired every hand held weapon. We fired the M-14 in recruit training and received familiarization with the M-16 in ITB. We fired machine guns, 3.5 and LAAW rocket launchers, and practiced with live hand grenades. We conducted assaults, learned the combat formations such as echelon, made night assaults, learned amphibious tactics, etc. We had chemical warfare training and got to sing the Marines' Hymn while in the gas chamber and crawl through the woods at night with fake bombs, rockets, flares, etc. while you try to distinguish the miles of fishing line left from the last 10 years of training form the new one which is attached to a booby trap.
From conversations with old buddies, I have learned that the additional training in SOI is mostly more intense training on tactics and combat formations. That and a lot more times through the booby trap courses, assault missions, etc.
Oh, we had courses on reading maps and tromped through the woods at night to see if we could take a compass and a map and find our @$$.
