Don't know if this is any help but changing from a 4.10 to a 3.73 rear gear increased stall by 1000rpm on our combo.
But that is somewhat artificial. The definition of flash is the highest rpm seen before the car moves. The car moves sooner/easier with the 4:10 than with the 3.73. That earlier movement might be more beneficial that then increase in flash rpm. Did the car improve in the 60’? Always trying to understand more about the converter  No, 60ft dropped a 10th. Slower by 2 10ths, Mph dropped 4 - 6 mph while rpm remained roughly the same through the traps. Slip increased from 10 to 17 %. I have since fitted another converter but no track time as yet. Sounds like the converter definitely not happy. I know people who have tried increasing slip % at the top to try and increase torque multiplication down track, but no real results yet. 10% seems a bit high. I’m at 4-5 % at the stripe. Which car? 8" ATi converter, it was originally specified for a 750 ish HP 528motor. It worked ok with the 572/580 motor and and 4:10 rear, showed over 900hp on a good day at the track going off the numbers and the weight (4023lb). Stall was originally 5200 (4:10) and it would go to 6000+ with the 3.73 gear. Data showed around 9 - 10% slip (4:10) which I was OK with as the car worked ok. I guess the change in rear ratio pushed the converter too far  We have fitted an ATi converter (9 1/2") that was built for our 655ci motor with 1000+ hp and a 4:10 rear, hopefully that will improve things.
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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