The sound quality will likely be inferior at the lower bias. Bias plays a huge role in an amp's sonic character. Try both but I bet you'll prefer the higher setting.
Target bias dictated by amp or by tube?
If my amp's (Line Magnetic 508ia) manual says to adjust bias of each power tube to 120ma on the front meters, but a set of after market replacement tubes (Cossor Valve 508) state their bias should be set to 65ma, which stat should I be following when putting in the new tube?