They are both good rigs, but I would give the edge to the
Kenwood...........I believe that the Elecraft is using a Mini-Circuits
Level
7 mixer, which would give an IP3 of right around +14dBm, assuming the 1dB
gain compression point is at 0dBm. The Kenwood uses that Quad JFET ring
mixer, which gives a slightly better IP3 of +20dBm

Elecraft IP3 is +21.6 dBm preamp off and +6.9 preamp on.... The best Kenwood
data is available on is the TS-870 and it's IPS is +16 dBm preamp off and +4
with preamp on.....

I personally don't think the TS-570 comes close to the TS-870 or the K2.
The K2 has, according to tests, one of the finest receivers in amateur use
today. Comparisons are available on the ARRL Tech web pages and on the
Elecraft web page.

Mike, W9WIS