I very much doubt you'll get an 80% overclock, not sure where you heard that from.
Your right though MSI Afterburner is a great tool for overclocking graphics cards, What I would recommend to do is:
1) Increase the Core frequency by 15Mhz in MSI Afterburner, Apply Changes.
2)Load up a game or benchmark and test for stability for 10 minutes.
3)If its stable continue to increase the core frequency by another 15 Mhz and re-test for stability
4) When it becomes unstable, either increase the core voltage (Vcore) or decrease the overclock to regain stability.
Make sure to monitor the temps, Make sure your graphics card doesn't reach temps of 90C+. I'd also suggest only increasing the Vcore by a max of 10%.