I just upgraded to QED Silver Anniversary Bi-wire and VDH D102 III HB interconnects.
The difference is quite subtle, but is definitely there. I did a slow transition to both, and the D102 III HB definitely improved the high-frequency clarity and a little of the bass response. The Silver Anniversary opened up the sound a little afterward, separating the instruments a little better, exposing the mid-range more, and improving the bass response a little.
The end result generally is a more smooth, detailed, and open sound.
I am thinking of putting off any upgrades for at least half a year, because this hobby is getting expensive!