Howdy fellow forumers! (not sure if that's even a proper noun?)

I'm currently shooting with a Nikon D610 and D600, and I'm shooting quite a bit of road cycling photography at our club and at the DISC indoor velodrome in Darebin.

My question: is it worth looking at a second-hand D3 or D3s, as they're a bit long in the tooth, but a pro camera body, and definitely faster than the D610? I realise the pixel count is half that of the D610 or even the newer D750. I can't (or don't want to) stump up for a new D4 or D4s just at the moment!

In addition, has anyone here used the D3 or D3s for shooting birds in flight? Good, bad, better options out there?

First world problems! :-)

Thanks!
Ern