Illuminas and RB springs will make your car sag. The MSP struts have a higher spring perch, which annoys the crap out of us MSP owners because we can't buy off the shelf struts and be stock legal for SCCA.
You have two options:
1) New MSP struts from the dealership or onlinemazdaparts.com and continue using the RB springs. The struts aren't cheap, and will run you over $700 shipped.
2) New Tokico Illumias and new springs. There is a spring comparison thread on here, you can just compare the drop of the RB springs to others and find the one that is the closest. Tokico also sells a "ILK" kit that has both struts and springs in one box. Not sure about the drop for the springs though.