But the 3.2E with the Prescott core is newer, cheaper for Intel to make, and it's one performance advantage is it has SSE3 instructions, where the Northwood only has SSE2, otherwise the 3.2C is the faster CPU faster.
They are really all enhancements to MMX (from way back)
All this really means is that they are special additional instuctions for mulitmedia, games, encoding and other Floating Point intensive tasks. (complex math type of stuff)
Programs do have to be written specifically to use these instructions, but if they know about them, they can use these faster ways of accomplishing their tasks.