Assuming a TC slip RPM of 200 after the 1-2 shift (I could simply test this on my car - it could be a bit more but I doubt it's less), here are some tables:
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Shift Before After w/ slip +200
1-2 5000 2656 2856
2-3 5000 3077 3277
3-4 5000 3480 3680
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Shift Before After w/ slip +200
1-2 5200 2762 2962
2-3 5200 3200 3400
3-4 5200 3619 3819
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Shift Before After w/ slip +200
1-2 5400 2869 3069
2-3 5400 3323 3523
3-4 5400 3758 3958
You can see how different the ratios are spread between the gears based on how different the new RPM is after each shift. I believe the way this model works is I am adding 200 rpm of slip after the shift, but none before. That may be exaggerated but probably gets the point across reasonably. If the slip was the SAME before or after a shift (and it is a very tight converter so maybe that is possible), I should use the non-slip numbers.
But here's the deal. Even if you run it out to the rev limiter (which is beyond the HP peak, in fact it is down by like 17 from peak), RPMs still fall to an RPM that produces LESS power than even at 5400 rpm. Even to get an ideal shift at 5400 (instead of beyond), the RPMs would have to fall to only 4200 after a shift. And you can see the 3-4 gets close because the ratios are in fact tighter there. But still not optimal.
However - there are also diminishing returns. What I did was look at average HP between the shift point and the new RPM after a given shift. Higher average HP should equal higher performance, most directly. Again, that assumes equal time at each RPM, at least within a given gear.
Here are some numbers.
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Shift Ave HP Ave HP w/ slip
1-2 5000 223 228
2-3 5000 235 237
3-4 5000 243 245
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Shift Ave HP Ave HP w/ slip
1-2 5200 228 233
2-3 5200 239 242.5
3-4 5200 246 249
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Shift Ave HP Ave HP w/ slip
1-2 5400 232 236
2-3 5400 241 245
3-4 5400 248 250
Side note, this is why aftermarket torque converters make such a huge difference on these cars. Between the wide ratio spread of each shift, and the very tight factory converter, a looser (but efficient) converter would really help keep RPMs up after shifts and get more power to the road.
My simple analysis is this:
Given the wide 1-2 spread, the higher the 1-2 shift point the better. Run it right to 5,400, which should be around 40 mph after 3.42s. It hits 260hp @ 5000, and revving 400 rpm beyond that HP falls to 243. However, after the 1-2 shift, engine power is around 192! If it shifts at 5,000, engine power after the 1-2 is even lower at 180.5!! The higher the better on the 1-2. Hence, average power shifting 1-2 at 5000 gives you around 228hp. But shifting at 5400 gives you 236. Is that a huge difference? No not really but it should be statistically significant.
The 2-3 is similar. Run it right to 5,400 in 2nd which should be around 76 mph after 3.42s. RPMs fall to around 3500 and average HP is 245. With a 2-3 at 5000 average HP is only 237 so another gain of about 8 hp. Probably still worth it. Even more so when you factor in time. So in the higher gears, you spend more time at any given RPM because the car is accelerating slower. You want to be at the highest engine HP possible at any given time which at 5400 is 243. After the 2-3 it falls to 3500 which is only 216hp. If you are going up a hill for example trying to pass someone, and you nail it and the engine downshifts to 2nd at 5000rpm to accelerate to 5400 (this would be a 70-76 mph example) you're averaging like 254 hp in that range. That is WAAAY better than if it could NOT downshift in which case that same 70-76 mph pass would take place in 3rd from 3060 rpm to 3300 rpm which has an average HP of only 198. That is a HUGE difference. It would totally change the character of the car, just by raising the upshift points and allowable downshift MPH. In other words, for every scenario that you can allow a full downshift and let RPMs run into the 5000 range, instead of only the next higher gear and RPMs in the 3000s, you are going to dramatically improve the performance of the car in those situations.
Now by the 3-4 shift you start to see diminishing returns. The extra average HP provided by a 5400 rpm 3-4 (vs a 5000) is only 5. I say only 5 because a 5200 rpm WOT 3-4 still provides 4 more HP. Not to mention, you are going like 115 mph at this point so hanging the engine at these RPMs is sort of not worth it. Just let it shift. I would propose something in the 5000 to 5200 rpm range for the WOT 3-4 based on this. After a WOT 3-4 at 5200, new RPMs are 3800 which is WAY better than the 1-2. Instead of falling down to below 200 hp, power is around 229hp after a WOT 3-4 @ 5200. Even after a WOT 3-4 at 5000, RPM drops to around 224. Still better than ANY 1-2 scenario. In fact, average power on a WOT 3-4, as shown above goes from 245 with a 5000rpm shift to 249 with a 5200rpm shift to 250 with a 5400rpm shift. Clearly not worth winding all the way out for a measly 1 hp average gain. But all of these numbers are better than even the best case 1-2 which provides 236 average doing a 1-2 at 5400, which is STILL less (by 9) than the WOT 3-4 at 5000. So a 5000-5200rpm WOT 3-4 should occur between 115 and 119 mph or so.
To accomplish this, it will require some trial and error because most of the shift point stuff is done by MPH not RPM. I will end up having to raise the fuel cut a little just to avoid accidently hitting the rev limiter before a shift can take place. Plus, again, I will have to account for torque converter slip but at those RPMs it shouldn't be much. At a minimum, if I didn't want to do all that, I could simply take the SS/9C1 shift tables and adjust for 3.42 gears (from 3.08) which would still probably make a pretty noticeable difference.