I may be wrong about this, but I believe that ring ratio is the speed of the interconnects between the cores, cache, memory controllers, and some other parts..
As for overclocking, my understanding is this:
-Higher ring clockspeeds decrease stability (especially if Cores and RAM are also clocked high).
-Higher clockspeeds improve performance, but not as much as overclocking the cores.
-Having a Ring speed higher than the Core speed does not improve performance
Basically, a 1:1 Core to Ring ratio is ideal, but can decrease stability. Having the Ring clockspeeds slightly lower than the cores is good enough and should allow you to push the cores farther.
Ultimately, if you're running at 4.3 Ghz Core and 4.3 Ghz Ring, that's good. If lowering the Ring to 3.5 Ghz allows you to push the Cores to 4.5, it will perform better, even though the Ring is slower..