There is no difference between hdmi 1.3a-1.3c, all hdmi cables, even the 1.0 ones can display 1200p@60hz no problem, the 1.3 ones can just go to 1600p@75hz and have a lot more support for stuff like bitstreaming trueHD, masterHD audio like david75 said.
Again, there are no feature differences between 1.3a-1.3c.

And about differences between cables, digital is digital, all the data that gets output, is the exact same data that arrives at the input.
The only bad thing about digital cables is, that if there is a fault in the cable, that data is lost forever.
The monster cable types do have perfect cables but they are very overpriced, so if you don't notice anything odd with your lowerprice cable, I say stick with it.