As for the Erie Canal path, the parts of it I've seen were nice, but not conducive of fast riding. The busy sections are busy, and some sections are poorly maintained. There are sections where you have to take the road. These are not always marked. We had to turn around a few times to get around an obstacle of one kind or another.
I was going to say something similar -- I would not want to use it for a nighttime speed trial. Not always marked, jumping on and off roads and not always a nice clear curb-cut, etc.