There is...not sure what it is. But Maximum Motorsports does not suggest them to be used with coilovers, which says to me that their valving might be weaker than the coupe versions.
It's been brought up here numerous times. The coupe springs are 600#/in front and rear whereas the vert springs are 500 & 470 F & R, respectively. The "softer" vert springs use shocks and struts that are valved accordingly.