Three horsepower should be plenty to do that job, assuming a good, sharp, dedicated ripping blade and a correctly set-up saw/fence. However, that "3hp" figure might be misleading. Lots of big-box saws advertise figures derived from motor specifications, not real-world usage. Kinda like how your car may have more hp than your tractor, but you wouldn't get much plowing done. I had an old Delta Unisaw with a 3hp, single-phase, 220v motor and I wouldn't think twice about a job like you have. One of those $100 direct-drive lightweights? Erm... not so much.

But that doesn't address your question. Yes, it's logical that the motor should be able to apply more torque to a smaller blade, but the arc of the cut would be longer, meaning more friction loss, so I think it wouldn't really help.