I think IRS is very very important. The SRA is at it's limit i believe

 

IRS and weight reduction... In that order.

Coming from a previous brand of cars that have some of the best IRS in the world - I can say imho that this is really what the Mustang needs to round off it's suspension and complete the car's 'sports' calling through all the platforms.. A Boss with a modified IRS suspension? That has the makings of a 'real' track car beyond it's current rivals and beyond it's current platform no matter that they have amazingly made an SRA able to swing with the bigger track themed built cars. Take a Boss with a modified IRS to Nurburgring please?? SRA should remain as a lower priced option absolutely!

Honestly a good IRS, and I really wouldn't care if the weight stayed the same, just don't get fatter..