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.
'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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