Shift Points -- Manual Transmission

[Subito Piano]

Hi! I just picked up a 2010 Accent -- manual tranny. The shift points in the manual differ from the suggested points on the speedometer, e.g., the book says to shift to 5th at 45MPH, but the speedo indicates to shift to 5th at 35 or even less. If I recollect right, back in the 80s John Muir stated that a Rabbit (1.8L) performed best around 1800 RPM, and of course the Accent has a 1.6L engine. Assuming fairly level roads, I'm wondering if I should not let it go below the 1750 mark on the tach, or the 2000 mark..or what? So -- advice from those familiar with HP and RPMs and the Accent tranny would be appreciated. (I DON'T mean to be snarky on my first post -- but please, if you don't have solid mechanical knowledge/experience, a reply would NOT be helpful.)

Thank you!!