On faster weapons 2 weapon damage is more significant;
1.4 speed weapon, 90 dps;
126 avg damage. +2 = 128. Or; 91.4 dps afterwards. (1.4 increase)
2.6 speed weapon, 90 dps;
234 avg damage. +2 = 236. 90.8 dps after. (0.8 increase)
4 to all stats is ~.6 dps increase from str, .13 crit%.
But it affects bloodthrist damage too, while +2 weapon damage does not.