Nice BCI!!
I disagree with the above post that size is the only way to tell. One look at the saddles on a particular snake and you almost know instantly if its a Suri, Guyana. Of course with all the inbreeding that can be hard to tell sometimes as well, but then there is saddle count, head shape....you get the idea.
I have seen 2 year old BCI females that were pushing 7 feet and ten year old male Suri's that were pushing 6 feet so I dont see how one can tell the difference by size alone.