Sony SAL 55-300 or Tamron SP 70-300 Di USD?

Have the SAL 16-50mm 2.8 and the SAL 35mm 1.8.  Agonizing over purchase of long zoom to compliment - and pretty much complete - the bag for now.  Price is not a factor here (between these two lenses), if I purchase the Tamron by 1/31 and grab the rebate (it would be just $50 more than the Sony).

Am enthusiast; photography is not an income source for me.  Read a bunch about both lenses, most recently CGarrard's review of the Sony.  Advice welcome?  harry