Our previous startup was with Rails and we did hit performance bottlenecks, even without Payments being involved. Consumers are very sensitive to speed, so that plays a big role in the decision as well. Team skills are adjustable - the founders are technical and the team is being built up hereafter. The big question is does GoLang still have any inherent issues that may conflict with the expected reliability of a financial company - is the Braintree objection out of date?