Yes, please turn the acceleration off.
You could deinstall the Logitech software altogether if you don't plan on using any of its features. The mouse will automatically "run" at 1000Hz and it'll use the standard DPI settings of 400, 800, 1800 & 3600.
The angle snapping has been removed in the second generation g400's, so when drawing some lines in MS paint it should look something like that: