More than 600,000 died either during the deportation or shortly thereafter.
Almost all of them were reserve Army officers (anyone who had a college degree was a 'reserve officer' under Polish law), academics, lawyers, etc. and their families.
The Soviet Union and Germany shared the same goal of exterminating Poland's culture and sense of national identity by annihilating her educated classes.
Apparently the Germans and Russians were equally culpable of disposing of the Poles.
There is a section in “The Rise and Fall of the Third Reich” that tells a grisly tale.
Otto Ohlendorf, Einsatzgruppe chief, recounts the massacre of tens of thousands.
It is a tough read.