If you’re getting jagged/aliased lines with your hard-edged brushes even while drawing at 100%, here’s your problem. Downgrade your Wacom driver to a previous version. 6.3.7-5 seemed to have no high resolution tracking support in Photoshop, despite whatever prior attempts to force it to work.
Your lines should always be properly anti-aliased while at 100% zoom as seen in Driver 6.3.6-3’s example. These lines were drawn very slowly to make sure the tracking was working correctly.
Test this yourself with your tablet to see if your drivers are working correctly!