Yes, the C springs will stiffen up the car nicely. They're springs designed for roadracing, so they're stiff on all corners (to improve handling as much as possible). Downside is if you're into drag racing, launching without lots of wheelspin becomes harder due to the aforesaid stiffness.
I love my C springs. They made a night and day difference. I would suggest while you are down there to replace the shocks/struts with some better ones. If you wanna go on the cheap like me you can find a nice used set of mach 1 shocks and struts for around $100 for the set. If you want the best get the koni adjustible or bilseins.