I dont see a stock cam or intake in your sig. Some people shift by feel and thats good once you figure out where the powerband is but if you are waiting until it noses over to shift, you are already to late.
First put a different tach in it cause the stocker's are usually inaccurate.
Second, to accelerate the car the quickest, you want to shift such that the rpm drops back to the peak torque range with each shift. Because of the transmission gear ratios, that means the shift point will actually be slightly different for each shift.
A stock 5.0 probably makes peak torque around 3600-3800 rpm; peak HP from 4500-4700 rpm. Using the gear ratios in the stock T5, that means a 1st to 2nd shift around 52-5300 rpm, a second to 3rd shift around 5000, and 3rd to 4th shift around 4800 rpm.
i did not read this whole thing, so i apologize if im being redundant. stock limiter is 6250. stock tachs are often off by a percentage - so at higher revs is when it becomes apparent that the tach is off (my stocker and AM are very close under 3K rpm, for instance).
doing SOTP testing works fine - as Jerry said in this or another thread, the tach (any tach) is a reference, just as an accurate tach is. that said, i sure would not being running around at higher rpms with an inaccurate tach. but im anal.
lots of folks have figured out what works and will know to simply shift at 6XXX rpm, per the stocker, and that works.