If you're fine with f/4 (50-135 + 1.4x TC gives you f/4), maybe consider the DA* 60-250? It covers a wider range, has great IQ and is smaller and lighter than any 70-200 f/2.8 (though it does extend when zooming). It's also not that much more expensive than the 50-135 right now.
I do own the Tamron 70-200 f/2.8, and I find it quite useful as a general purpose telezoom with good IQ and speed for low light. It is actually one of the smallest and lightest in its class, but still big in absolute terms of course. It also is one of the fastest and most accurate focusing screwdrive lenses I own. It will not focus properly in Live View mode, though, and MF is pretty meh. It's also not weather sealed, if these things are important to you.
Last edited by Cannikin; 07-17-2015 at 01:26 PM.