I bought a set of the SVE springs and thought they would be as low as my Sportlines. They are actually a bit taller and when I installed them on the rears & dropped the car back down last weekend, it sat to high for me, granted they may have settled some after a while but I pulled them back out.
I wanted to be a bit lower, not higher, so I ended up pulling all isos from front and back and putting the Sportlines back in. It now is, to me, noticeably lower, netting about another 1/4" - 3/8" drop and am very happy with the results. A short test drive produced no ill effects.
I may sell my SVEs or just keep them to "modify" if I want to go lower in the future.
Install them with no isos or even with just the uppers. They will sit just as low if not lower than your sportlines and will feel better on the road.