Don't bother with ln2 mode, its only of any use if you are using extreme cooling and have the custom version of afterburner extreme to push the voltage above 1.35v.
Normal bios, fully unlock afterburner will give you clock limits you will never reach with 1.35/1.7v voltage caps with 20% powertune and +30mv aux power.
As for clocks its system subjective imo. PSU's will need to be beefy and using a decent motherboard, for example my ud7 has optional power inputs to provide extra power to the pci lanes, I think little factors like this can help.