I decided to run my math again with my own 66 Mustang and its 289. I've been debating back and forth about whether or not to keep the C4 and stock 2.80 gear it has now or swap in an AOD with a 4.11 gear. It kinda shocked me how little the difference is between them.
From a dead stop, 4k stall converter in both.
Big advantage to the 60ft of .23 seconds for the AOD, but then look at the 1/8 and 1/4. That advantage doesn't carry out. The 1/8 advantage is .33 seconds and 1/4 is the same .33 seconds. The C4 with the 2.80 gear stays in 2nd gear the entire way from about the 330ft onward.
From a 40-85 roll.
A difference of just .035 seconds. Not even half of 1 tenth of a second difference in a roll race.
Both of these cars would cruise right at 2600rpm @ 70mph. Well... the AOD would in lockout. The C4 with a 10" 4k stall would have about 10% converter slip cruising down the highway so it would be more like 2860rpm.
A 4k stall converter from Hughes or TCI for the C4 is about $550-580. No 4k stall lockup converter is readily available on the shelf for the AOD which means a custom converter in the neighborhood of $800+. I could buy a 3000-3400 stall converter off the shelf with lockup for about $500 but then I'd most likely lose all of the 60ft advantage of the AOD to begin with.
On top of that, I already have the C4 and in stock form, can more than handle the power of this engine. An upgraded valve body ($300) to firm up the shifts, stronger input shaft ($150), 4k stall converter ($550), and deep pan + fluid cooler ($200) to keep heat down with the high stall on the highway would be less than $1,200. With the AOD, I'd be looking at $500-600 for a used AOD, plus another $500-600 for all the swap parts such as a TV cable, crossmember, trans mount, linkage, etc... another $150-200 for a shortened driveshaft, $150 for a stronger input shaft, $400 for a valve body to eliminate the dreaded 3rd gear partial lockup, and then still need to cover the cost of the converter, cooler, and 4.11 gear. Due to the extra width of the AOD, the vast majority of the headers and mid-pipes on the market won't fit around it so you either have to go with a full setup of JBA headers and mid-pipe ($800+) or have something custom made.
I think I'll stick with the C4 and 2.80 gear.