I got a chance to test the FC spec tire at Carolina Motorsports Park (Kershaw).
I ran some used R35 Hoosier radials and then switched to the bias R60. We had to make the change quickly so camber was just a SWAG and there is room for improvement based on the tire temps. The balance of the car and feel of the car were essentially identical.
There was some rain early in the day that meant that the track improved as the day went on, and it was my first ever trip to CMP, but I was 2.5 seconds quicker on the R60 spec tire. Wear was very good. The outlap had good grip.
We put about 70 miles on the spec tire. I think that we had a bit too much camber in the LF, but the tire held up just fine. I expect to easily do a majors weekend on one set with the ability to test/practice after. With a slightly reduced pace, two or more weekends would be possible.
I'm a long time Hoosier cheerleader, but my on-track experience with the FC spec tire was better than I expected.