I wouldn't get higher than level 2 for D4, and if I got level 2 it would be mostly for the special ability.
I've never found reliable information for this, just going off my own limited experience. Popular opinion rates them a bit higher than me but still I think most would agree lvl 3 for D4 is excessive.
Last edited by w_alloy at 1/3/2013 5:13:54 AM