HD4870|HD6970|1025/1505|P6199|Core i7 920@4.25Ghz
HD4870|HD65870|1069/1357|P5379|Core i7 920@4.33Ghz
So, HD6970 with 16.4% Core OC and 9.4% Mem OC beats HD5870 with 25.7% Core OC and 13% and slightly higher CPU Frequency BY 15.2%
Will try Stock now and tell you the difference
:)...