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Shifting at redline is a horrible idea on any vehicle that's remotely stock... ESPECIALLY one that's 25+ years old (even worse if it's a '89+ MKIII). If you believe that the 7M (or any engine which came in any generation Supra) made power beyond the rev limiter you'll hopefully be wise enough to heed the rule of thumb that you should shift 5-10% short of redline as bouncing off the limiter will definitely cost you the race (and in this case quite possibly your engine).

The best point to shift is always a topic of considerable argument. The smartest thing to do would be to take advantage of modern technology, get on a dyno and check out the performance per gear and watch for overlap. The optimum shift point is going to change as you accelerate from a stop and the dynamic of the load changes. Initially you'll want to favor the optimum torque RPM and as your speed increases move the shift point north up to the peak HP RPM. Now, you don't want to shift right at the peak of the TQ curve. For example: if you shift out of 1st right at the peak or the toque curve you'll be dropping into 2nd a good deal further down the curve and have a good amount longer to get back to that peak power level. Shift out of 1st a few hundred RPM after the TQ peak and you'll only have 200RPM to get back to peak in 2nd. Torque and HP generally drop off slower than they're reached, don't ever shift at or before peak TQ and don't shift after peak HP (there's nowhere left to go but down).

Looking at a couple stock 7M-GTE dynos, the peak torque in 4th gear is around 2700-3200RPM and peak HP 5000-5500RPM. The MKIII doesn't pull for shit after the mid-upper 5000's and I wouldn't hold it past that.