I'm coming a little late to the party but congrats!! And just to ease your mind further, I have a very good friend who is an amazing bike wrench and does custom builds for a living. He loves SRAM and says it's a way better deal than Shimano and also far more reliable. As for mixing the 2 go ahead. And I would also go for the 11. I have the SRAM 11 -27 on my compact double and I love it, the 11 does make a big difference.