While CALIGULA is definitely a well made film with well known actors, I definitely put it in the porn category as there is plenty of explicit, hardcore sex in it. Great film nonetheless.
As for FORCED ENTRY, it's also definitely a porn film as well. It's quite nasty and has some fairly graphic gore scenes, but it's the main character's level of sadism and language that pushes it WAY over the top. Harry Reems disturbingly vile in this one, so much so that it almost makes you wonder about him in real life. Worth a look for historical purposes if nothing else. It was just recently released on DVD in fully uncut form as it's been butchered over the years.