I've been experiencing occasional delays in the game during ranged combat and using the inventory menus.

1. Shoot an arrow, and after a few seconds, it finally hits, as if lagged. I sneaked up on a bandit, aimed, and fired. Nothing. A full 3 seconds later, the arrow hit.

2. Using the menus, the graphic of the item (weapon, armor, reagent etc) appears on the screen a second or two later whereas before it would be instantaneous.

Most of the time it's a symptom of disabling Vsync (iPresentInterval), have you done that mate?

I actually enabled v-sync to stop screen tearing after the 1.5 patch so I don't want to have to turn it off now. If that's the cause, I can live with the slight delay.

No mate, having vsync off can cause your issues is what I'm saying

If you have it on, I'm not sure what it could be sorry.