Worth mentioning, that ALL bodies now have great high ISO performance, all superior to the best of the worlds ISO 5 years ago. To scrutinize the differences of quality at 12800 + gets quite pedantic. The fast lens will open up much more than any difference in noise gain on modern sensors. If low-light autofocus is important, should stick with DSLR.

But yes indeed, matt's suggestion is a pretty solid choice too. The tamron 28-75 f/2.8 is the gem for cost efficiency, but 28 can be kind of narrow a starting focal angle for many. Perfect for me, some may prefer 24mm or less start (17-50 f/2.8 option)