[M_Six]

Thanks, Dave. The 1Dx is well out of my price range, but the 5D MkIII and 1D MkIV are attainable. As tempting as the current Amazon sale on 5D MkIIIs is, I'm pretty happy with my 6D for everything except BIF shots, especially when using the 400 + TC combo. For that reason I'm leaning towards a used MkIV as my dedicated birding rig. It would give me the faster, more accurate AF, faster FPS, and a slight crop advantage.