They are two entirely different animals.  Both extremely attractive.  Which is "best" for you depends on the type of operating you do.  My guess is that a hard core CW operator and/or contest operator will prefer the K3.  For portable and QRP operation the KX3 might be preferred.  For casual rag chewing they might both be more radio than "needed".  However, I recognize that few of us make our ham radio decisions based on need. 

I did not know anyone compared the KX3 to the IC7000.  I have been running an IC7000 mobile for 5 years, and if I had to replace it soon I know of at least three radios that I would consider over another IC7000... and the KX3 might make #4.  When I talked to Elecraft about the roofing filters for the KX3 they could not tell me much about bandwidth, shape factor or cost... but said that roofing filters will be a MUST, as the KX3 is a SDR, unlike the K3. 

Until units are actually in the marketplace, and carefully evaluated along with the obvious options, and pricing is firm, questions about how it compares to the K3, Ten-Tec offereings, or high end Icoms are moot.  All I was able to learn about pricing was that they are aiming at "under $800" for a bare KX3.  With the 100 watt PA and the ATU and at least one roofing filter, it may still be less than a basic K3/100... but does not appear to have the expandability. 

Bottom line is... we can ask questions... but we can't get many REAL answers... YET.

Best to all,

-Dave-
K9FN