One or 2 extenders with 500mm F4 IS, 1D MarkII. iso400, Gitzo 1325 or Feisol 3402 tripod, Markins head, Wimberly Sidekick, BetterBeamer flash extender, & CP-E3 battery pack.

With Tamron 1.4x extender:

With Tamron 1.4x & Canon 1.4x extenders

USM test of 2 extender shots.

Left panel: 100% crop w/out USM.

Right panel: 211/0.5/0 Unsharp Mask sharpening in 16bit RGB space.

These pictures were taken here: