Depends, if waiting is the issue, did you just now started wanting a lens like that and really can't wait? If you thought about it for a while already, IMO there is no harm is waitng a little more (unless you have something you "have to" take photos of right now).
TeamSpeed wrote in post #16709533
Agreed, I would put the 50-500 OS against the Tamron as more of a match than the 150-500.
Depends on market/country I guess. The Sigma 150-500mm is approx 30% cheaper than the Tamron here. The 50-500mm is about 70% more expensive (than the Tamron). That makes the 50-500mm a poor value for anyone who doesn't absolutely need the 50-150mm range on such a lens.