No you won't get the same results, your amount of pixels left will be much less if you crop. On the other hand, the quality of the image on the 24-70 is superior to that of the 28-300 without talking about its possibilities in low light. To have a f 2.8 lens allow for more flexibility in low light.
You have to ask yourself what kind of pictures you take. do you do portrait? landscape? wildlife?
If you want an all around lens to travel and you don't care too much about the small details of the picture, or if you do lots of wildlife than you may want the 28-300
But if you do landscape or family pictures you are probably better off with the 24-70 specially with such a good camera, you probably want this quality not hindered by the lens you choose. I already have the 24-70 with my D600 and I am very satisfied.
Thanks Micheline. To answer your question I take landscape and indoor gym photography