Nex-5N vs OM-D, D300 user

I currently have a Nikon D300 with various fast glass (85 1.4, 50 1.4, 70-200 2.8, 17-55 2.8).  I will keep this setup but looking to go smaller/lighter and gain a little better high ISO performace.

I typically shoot portrait in studio (probably still use D300) and sports action (tennis, vball).

Looking at Olympus OM-D and Sony NEX-5N

Would appreciate comments about Olympus vs Sony along with D300 vs either of these....Thanks.