less rolling resistance is all about your tires mate, not your rims or hubs. My DA 7400 cranks are 32 years old. 🙃 sons and gran compe hubs is a good solid choice (I assume you’re not talking about the gran compe pros, based on your budget) I see nothing wrong with that upgrade. If you want better power transfer than yea a better crank is the ticket. I’m assuming you’re running 25mm tires? 50:16 would give you about 83 GI. If you want a smoothest possible drivetrain with reduced fiction, you need to go bigger. Period. Larger sprockets=More efficient. That comes at a cost of weight though, at least when you’re running 1/8”. Something like a 53:17 or 55:18 would be around the same GI. When I want to put power down I run 61:19 (87 GI) & 61:22 (75 GI) for regular riding.