Stock tabs are fine - they were tested in this thread on RC Groups. See #18 for discussion on tabs - he calculates a tab resistance but his testing is for his planes current draw, 35amps.

This thread is also a great reference on building and using a123s. It encompasses about everything there is to know about rc useage of a123s, either directly or with links to other material.

http://www.rcgroups.com/forums/showthread.php?t=599316