So I ordered some 5355 Xeons to upgrade to an 8 core machine...everywhere mentioned to get some long either 3mm or T15 screwdrivers...I have 2 questions, 1) Which one is better 3m or T15...obviously both will work but what is the screw really? and 2) How long of a screwdriver do I need for this job? All replies are GREATLY appreciated!