Help me decide

I went out with my 50mm 1.8G and 70-300VR and took some nice pictures(for an amateur and my first time) that I was happy with. I liked both lenses. I was about to buy a 17-50 2.8 Sigma based on some real good reviews and seeing some great pictures. Here is my dilemma. I also want a 70-200 2.8 Sigma (also based on looking at some great pictures). I thought about what I'll be shooting the most. I'm going to motorsport events, sporting events, airshow, zoo and I like taking portraits. 70-200 2.8 can do all those and 5.6 aperture might struggle with subject isolation or even the ability to shoot in lower light. I was still able to get some nice bokeh with my lenses, but it might be harder to do at events. I had a good experience and I learned a lot with my current lenses.

Here is the big question. Which would you rather have?

Nikon 50mm 1.8G
Nikon 70-300VR
Sigma 17-50 2.8

or

Sigma 70-200 2.8

I'm still within my period to return my lenses. I have a D7000. It will be a pretty much an even exchange. Or I can buy a Sigma 17-50 and have the 3 above. Let me know what you guys think. Thanks in advance.

Here are some of my pictures.