What Hondo6 said.
You've got the hard-to-aquire 7900 dt shifters, so why not go 10 speed. I have no problem with a mixed older 8 speed crankset with 10 speed rear.
Shimano 105 10 speed FD, GS RD, and brifters with Ultegra 7400 crankset and an 11-36 cassette...for that nearby bit of 19% grade.