I have crunched the numbers, as I suspected it looks like I will have to run to redline in all gears. I have been using 7500 rpm as a fairly safe redline, that's 600 rpm past maximum power, although I could and have run above that in the heat of the moment. You can see from the numbers that in most gears it never gets higher wheel torque in the next gear up than in the lower gear, that's what I meant about graph lines not crossing if it was plotted (see example graph of what ideally it should look like). Apparently it's not uncommon for this to happen, it depends on the torque curve, gearing etc.
My car is close but not identical to when this dyno run was done, but it shouldn't be too far off. Also, the actual torque numbers in the spread sheet are about 13% higher than true because I just used the numbers off the dyno sheet which are in Nm at the wheels, so the high of 125 should actually be about 109 lbsft at the flywheel, but that shouldn't alter the shift points. As the readout cuts off at 7250 rpm I just estimated the torque for the last 500 rpm, but it should be in the ball park.
Just looking at the numbers again. 1st to 2nd ok at 7500. Third to 4th change and 4th to 5th probably ok at 7500 also.
My Torque at the wheel, very top line.
What it should look like when torque in next higher gear passes previous gear
By the way, my gearbox has the lower 4 gears from a Fiat Regata 100S (1600 twin cam), but retains the std X1/9 5th gear. this gives a big jump between 1 & 2 and between 4 & 5, but close ratios between 2, 3 and 4 which are the most commonly used gears on most race tracks I go to.