Pulled up the review of each from Car and Driver. They have the difference at 1.8 in the 1/4.
Killer for the Mustang is the near 3600lb curb weight.
I'm surprised though. These things were very well welcomed by the community. Didn't expect the sales numbers to be that low. I agree with the pricing aspect though. You'd think a mid to upper 20k car would have slightly more power.