my information may be a bit dated as I haven't raced on-road in 6+ years, belt drives have pretty much dominated the market in recent years because they tend to produce downward force (increasing grip) on hard acceleration where shaft drives tend to produce torque steer on hard acceleration. A properly engineered belt drive that is tuned properly can be comparable in efficiency with shaft drives. Older belt drive designs were lacking proper tension adjustment and folks were spraying belts with WD40 to loosen them up to help free up the tension to improve efficiency. Not sure where Xpress falls into the mix but I would do some research to make sure they have worked out any kinks on their tension adjustment.