Boundries and Thresholds for SharePoint 2013

SP2013 recommends a max of 10 million per index partition, the same as SP2010.
Streched farms are supported in SP2013.  Stefan Gobner


More Info:
SP2013 from MS SP bountries and thresholds
SP2013 Search
SQL Server IOPS Calc
SP2010 Notes of Thresholds
Comparison of SP2010 vs SP2013
Comparison of SP2010 vs SP2013
Comparison of Foundation, Standard and Enterprise editions of SP2013