Thanks for good replys!
OK! then it was a little bit better than I tought 
nice to hear
We don't have separate subnet for this, same subnet for everything in vSphere. Should I still have two switches to separate the traffic?
How big impact is it to do this during office hours? Should I first create a new switch with management and vMotion and then remove manage network from vSwitch with all VM machines on?
I did a quick check and one NIC on every host didn't have that much KBps using so I think it should be fine.
I have two blades switches with 2 NIC's from each switch then I have two switches connected to the blade switch on the "outside".