Logitech China even has an official tip on why G403 users can't draw a horizontal line.
I believe G403 is not the only mouse that would have this problem. If one is using IE3.0, he's likely to have the same experience.
It's just that G403 is so hyped. People have really high expectation of it.
So many people put interests and attention into it. So many bought it even if they never handled a gaming mouse before.
People notice some issues on G403 and yelling around every forum, saying they are cheated by Logitech.
It's just because they never really paid attention to a mouse like they did to G403. It's not G403 having the issues.
Get higher speed memory and manage to run your game at 240+FPS with all kinds of v-sync and buffering turned off before you talk about mouse precision.