I noticed a similar variation when searching for the correct GTLs. It didn't occur to me to try to use it for tuning!
So, you're suggesting that for a specific set of voltages, the GTLs that give me that max GFLOPs/min Times in LinPak (over several trials -- I usually run 15 before switching to prime95) is the sweet spot? That I should tune for that? See if it's stable and if not, move on?