I've been playing on Survival Difficulty for I don't know how many hours now and was never really sure of one thing. Now I know that higher difficulties do not inherently impart more XP per kill. However, when I initially went from Normal to Survival, I felt that I was encountering higher level variations of enemies which would of course mean the chance to gain more XP from those specific enemies. I don't know if I just imagined this but does anyone know for sure?

You don't encounter any higher level enemies than you would on normal, I don't believe, they just have a lot more life and are harder to kill.

Thanks for the swift reply. I knew there was a possibility I was just dreaming it up. I'll probably end up dropping down to Hard simply because I'm tired of all of the bullet sponges, lol.

I believe that on the higher difficulty setting, apart from the damage modifiers coming into affect, the chance of your opponents being a higher ranking variant increases.

You get more XP for killing a tougher variant.

One thing that could muddy the waters is that as the level you reach in the game goes up then some tougher enemy variants are introduced.

For instance on reaching, say, level 35 a new opponent rank of a particular foe could be introduced that has higher base health and earns more XP when killed.

An example, for super Mutants there are 10 different ranks ranging from standard to Warlord.

Standard earns 7 XP while a Warlord earns 91 XP

As your game level increases you will see the higher rankings.

Warlords don't appear until level 68.

At level 16 skirmishers are introduced

At level 22 Brutes appear

at level 28 Enforcers are encountered, and so on.