Terrible stuttering and bad allocation error

The skill stutter problem when you first use skills is because we're not yet able to preload some of the effects they use (The glow of the skeletons, for example). If it is very slow on your PC, I'd suggest just casting the skills when you first start the game - They should be loaded into memory for the rest of your session.

As for the "Bad Allocation", is this something that happens a lot? You can try running the Pack Check and removing any corrupted files.

At the moment you can add --nosound to the end of your Path of Exile shortcut if you want to disable sound entirely - Though reducing the volume sliders to 0 should do this. I'll have to confirm that though!

The client log file might only cause problems if the file is very very large - Writing there shouldn't cause any noticeable delay.