The prima facie case for free will* is that it feels free. If you can predict the action before the feeling it removes that argument (unless you want to invoke time travel as an option)
*one of the predominant characterisations of free will, anyway. I'm a compatiblist, so I have no issue with caused feelings of decision making being in conflict with free will. I also have a variation of Tourette's, so I have a different perception of doing things wilfully when compared to most people. It's really hard to describe how sometimes you can't tell if something was tic or not.
Hm, but maybe you can predict the feeling before you can predict the action. Checkmate atheists :)
(for the record I am also a compatibilist)
I don't see why having some latency in the path of free will makes it no longer free. Before my arm moves up, there is a motor neuron that fires that is always correlated with my arm moving up; doesn't that just mean the free will occurs earlier in the process than the motor neuron firing?
There are a lot of things I feel that end up not being "real," like embarrassment, a failure. and anxiety. Why should free will not be like any of those?