Currently have the grid snap size to 8 from 16 that is the default..

Its much better as 8 but its not perfect. There are many times where the wire is not straight.

So how about when you hold shift or so and drag selected nodes, to disable grid snapping? (set it to 1)

Very simple, and it would be a small improvement. If i were a ue4 dev, i would totally have implemented that feature.