First time overclocking. Temp hitting peak of 89C on one of the cores after 8 hour Prime 95 blend. Is that stable/safe?

This is the first time overclocking my 3570k with a z77 Extreme4 motherboard and I'm trying to follow the guide on the side bar. I'm currently at 4.2 ghz with my voltage at -.075. Should I continue to decrease voltage to try and get temp down or until I BSOD? Sorry if the OC process is straightforward, I'm just trying to get the gist of things