FWIW the 2500k I bought ~3 weeks ago is C-batch, L041C119. Takes 1.54V Vcore to hit 5.2GHz (not stable).
Someone earlier posted 4.5GHz with 1.2V, this one seems nearer 4.1GHz at that Vcore. :(
At 1.2V seems okay for Linx @4.2GHz
http://i1181.photobucket.com/albums/...th_42_Linp.png
But Prime with same settings above using less power and lower temp fails @4.1GHz.
http://i1181.photobucket.com/albums/...1_Prime264.png