That's a big call! I don't know if I'd be brave enough to promise making devs 50% more productive. Definitely a good consultancy sell but I wonder about what the delivery would actually be.
I have a pet theory that the standard practices in software development actually reduce productivity, at least in the short term. From my experience, the sure fire way to get teams to be more productive is to first hire great people, then to empower them and make sure their morale is high.
Not sure how I could do that on a consultant basis. I can imagine how I'd bring tighter project management in, and make sure people are doing what they're best at. But actual long lasting productivity of a team I don't really directly manage?
Someone who can do that is a wizard.