I just completed the same job on the same machine. I used the hairdryer/Goo Gone procedure. The glue was very tacky on this particular game. I've removed mylars before, but High Speed was the toughest for me. In the end I had to use a combination of Magic Erasers and Goo Gone. This worked, but it took some time. If I used the freeze spray method, I'm assuming the same thing would have happened with the glue being left behind, so the glue removal would have been the same issue.
As far as artwork being removed with the mylar, it wasn't too bad. It was the glue removal with all the rubbing that took a bit of paint off around some inserts. Touched up around the inserts in question,as well as a few bare areas around where ball drops off the ramp and habit trails, and then clear coated with auto clear.
It turned out very nice, but I see some separation of clear coat around some of the inserts. This is not good. I highly recommend removing and re-gluing all your inserts before clearcoating your playfield. I did not do this :(. It's not terrible, but not perfect either. I've learned the hard way this time. I'll address the inserts from now on!
Here's some pics!
img_1748.jpg (Click image to enlarge) IMG_1732.JPG (Click image to enlarge)