Well, I'm back to Nuendo 6, from Cubase 7.5. ASIO Spikes.

Have you tried increasing the audio preload amount?
Look in Devices/Device Setup/VST Audio System.
I think by default it is set to 2 seconds. You can up that to 6 seconds total.
I have mine set to 3 seconds I think.

Try increasing it by one second steps and see if that helps.