What, out of curiosity, does winsat mem now give you? That'll probably help us judge whether we're good, or want to 'poke around' a bit more ('course - your tolerance for the fiddling is the main factor! )
Well, all in all, not that much boost - we could certainly go further, but if you're happy, I'm happy! I doubt you'd actually see, subjectively, the difference from further improvement unless you take to transcoding video - that 'eats' horsepower... For the additional sticks, most likely just need to add a tenth to MCH voltage - to 1.2V...