Big concern here i had one go out on me putputting around only doing 40mph and it went,, luckily i shut it off immediately towed it to my buddies shop and no damage because i shut her down quickly. This could really be bad you could suck a valve or worse if a spring goes bad, a valve can drop destroying pistons and even cracking blocks then you have to go into motor $$$$$$:down:. Ive heard a alot of other guys this has happen as well to. I upgraded mine to Pac 1218 i know some guys use the dual springs but on a stock valve train i think it puts more stress on other components being they are stronger. jmo.
Be safe than sorry. If you search the forum this has happen to other z06's.