The difference is Enhanced Body Technology (EBT)
The New Power Pro
Shimano bought Power Pro in 2009 and quickly made a lot of changes. The original formula that put Power Pro in the front of the spectra trend has been updated. The new Power Pro still has the body to make it cast better than other softer Spectras, but the line no longer has the pronounced waxy feel of the old Spectra. The new spectra is also braided tighter which reduces its diameter. This prevents the spectra from flattening out when being fished which allows it to cut the water better. The smaller diameter also allows more spectra to be put on a reel...or heavier spectra to be wound on in place of the original lighter line.