We use Eye fi cards reqularly in a CF to SD adaptor. Both the new x2 pro and the older blue one cant remamber the name of it.
We are running an N class router so transfers are quick, I have never tried it on anything slower so can't comment but we do usually only shoot medium fine images when using it but I have ocasionally shot raw and again 15 seconds isn't too long to wait saves pulling the card out all the time.
It isn't 100% perfect everytime but we know what the problem is, if you view the images in camera while it is transfering it stops the transfer and takes a while to resume again.
The other issue is it has to reconnect everytime the camera wakes up from sleep again it just delays the first transfer to the PC usually going again within a minute.