In my opinion if your driving for performance than you are usually running in a lower gear to keep the RPM's up. Sixth gear would probably not even be used.
Ya I only have 5 gears now but I will cruise around in 5th gear at times at 30-40 MPH to save a little gas. Seems to be the same with a 6 speed just cruising at 55-65.
You can't be lazy when it comes to a manual transmission. If your complaining about having to shift at highway speeds what are you going to do in bumper to bumper stop and go traffic?
01 ZX3 - 07 Ranger FX4 - 68 F250