105 on this bike will be great. The SLR brakes are light years ahead of the Speedy's and the drivetrain is much better than Mistral. It will work with the Mistral crankset and it is mostly a matter of preference. If you like Biopace, the 105 is the way to go, otherwise, the Ofmega will work. I am fairly neutral about Ofmega stuff, but there are a lot of people who do not care about it and I have not heard of a single person who would outright recommend it. (On the other hand, those Modolo brakes are a POS.)