It turns out the new data Rob Sherwood posted is his personal unit that was tested along side of mine and I posted that info early on in this thread. Both receivers were tested under identical conditions and his was checked again at a different lab and produced the same results. Rob initially put my radio on his website as the lower numbers are probably middle of the road for this model.
The discrepancy seems to be the actual A/D converter chip in each radio differs from unit to unit and that is probably responsible for the varying levels of measured performance. You might get a radio with really good performance worst case, or you might get a radio with stellar performance if your lucky.
Rob seems to think there is little difference in actual on air performance when you get into these upper receivers, even with the 10dB or so difference in close spaced dynamic range. Personally, I think someone could make a living testing R8600s and charging extra for a premium unit.
Here is a comment Rob had comparing the R8600 to earlier Icom models: "VHF/UHF dynamic range (DR3) and reciprocal mixing (RMDR) wide-spaced performance is similar to the IC-9100. Close-in, however, the performance is significantly better. HF performance 10 kHz – 30 MHz is state-of-the-art." In other conversations it was mentioned the R8600 is a better receiver than the R9000 and for a lot less $$. You might read that pdf again in this thread that has some comments on VHF/UHF performance.
prcguy
Got to see one close up here at the Orlando Hamfest. Wow it is tiny. I think a dozen of those would fit inside my R9000!
Please keep us posted as to Sherwoods personal opinion on this radio. I think what I glean, at least in comparing with the IC-R9000 is that the new receiver has much improved dynamic range and lower LO noise. Would I be correct? And are these strictly HF assessments, not the UHF and microwave bands?