blacktop rods are weaker and will snap at higher revs, at which revs depends on the rods and length of which it's reved there. Silvertop rods are tough and will be able to handle 8500 RPM all day
for your 7a bottom end you need to use 7a rods.
not using vvt but having a 7a bottom end is contradictory. Both give you more low down power without a top end gain.