1.) I don't recommend EVER following the CR guidelines exactly when dealing with classed NPCs.
2.) Drow are often "overpriced" in CR/ECL for what they give
3.) While I'm saying they could be considered lower CR than what the book says, I will say...if that template is what i think it is (+6 str and con, some other goodies, all for +1 LA), it's the one I banned on the spot upon seeing for being just plain ridiculous. Not as stupid as the Feral template, but that's hardly saying much.
I learned earlier in my current campaign that CR doesn't always translate - especially when you give a CR:7 or 8 type of monster a level or two in a class. It's usually not the equivalent of bumping up the CR by 1 or 2.