D600 + 70-200 or an aps-c +85/1.4 for indoor tennis?

I have recently purchased a d600 along with a 85/1.8 lens from nikon. I really like the camera and the lens. I have one problem however. I really enjoy shooting tennis. This is usually indoors in poor lighting conditions.

I have noticed from testing that a 70-200 coverage on a ff camera is basically perfect for indoor tennis. However an aperture of 1.4 would also be very useful.

So I wonder is it worth it to get the 70-200 VRII or should I maybe go for an aps-c and some fast primes or maybe stick with the 85/1.8 and crop?

Anyone with a similar problem?

If I am shooting at 2.8 or above iso will have to be above 6400 or even well above.

Here are some shots. Two at 2.8 and iso above 6400 and one at 1.8. All of them are crops. Less cropping on the volley. How much better will the iq be with the zoom when not having to crop?