Spent a bazillion hours in the lab in college looking at stuff. Spent so much time looking at morph stuff under a microscope IDing critters and so on my eyes still hurt, and that was over 20 years ago. Of course I may just be getting old too. IMO, If you have a 100% count on all morphological differences in a given species, then make it a species. If it aint 100% it is a variation.

http://www.thefreedictionary.com/subspecies

I know more is needed in the definition link, but like I said, I keep it simple. I like finality.