Stock settings are best. Lowering the dwell won't really do much except put less stress on the bumper o-rings. If you lower the dwell enough you might get more efficiency but it may affect velocity consistency/reliability.
Follow the Vanquish Tuning Guide for the results you want: http://www.pbnation.com/showthread.php?t=3982778
The spring is only to help with First Shot Drop Off (AKA Bolt Stick). It doesn't noticeably affect anything else. If you remove it you should raise your ABS Dwell (Anti Bolt Stick Dwell) setting to compensate for removing the spring.