It's not that it doesn't interfere too much, you use the missile attacks mostly because they have auto-aim. It's a design decision which makes them stand out amongst other attack types. And while yes, you have to aim to actually hit things (moreso with ranged lob attacks, ray attacks and AOE attacks), it's hitting stuff is very easy. The skill set you have aquired while playing FPS games is not something you'll use too often in Lichdom. Sure, that's not entirely true, but the game is just very different.

I've got GeFoce 560ti with 1 GB and it works fine, albeit not with everything maxed out.