Max Motorsports sent me 400/600lb front/rear springs with their kit. They were quite stiff, probably a good combo for the track or if you have smooth roads. I swapped them out for 300/475 springs which are more forgiving on rough roads.
It says right at the bottom "Not for use in automotive applications". Not sure why.
I've had one of their Group 48 Restart batteries in my car for about 5 years now, no issues. The car cranks way faster that with a lead battery. Only downside is you don't have much reserve capacity so you have...