Are we talking on the street?
Then the manual will very likely be slower.
Here is just one reason;
With the close ratio, the gear ratios are
2.87-1.89-1.28-1.00 the od ratios are one of .68/.72/.81
Lets say you are currently running 3.23s in the back with your 727.
Assuming no wheelspin, Your acceleration will be directly related to your roadgears times your engine torque. With the auto, your roadgears would be
7.91-4.68-3.23. However, your convertor has a torque-multiplier inside it that continuously varies the output torque greater than the input torque, by a factor of, at WOT, of close to 2:1 with the vehicle stopped, and automatically decreasing with roadspeed to end up near 1.1 at say 100mph. Let's say in your case, it starts at 1.8, and averages to 1.3 in Second gear. Your new roadgears are
14.34 at a dead stop, diminishing to say 11.8 on the 1-2 shift, then averaging 6.08 in Second and averaging 3.55 in Third gear. All of these are at WOT.
Here they are in a string;
14.34-11.8-6.08-3.55, diminishing to say 3.39 at cruize
Now lets look at the 5-M/T; Roadgears are
9.27-6.10-4.13-3.23-2.62 (.81 od)
As a streeter, you are only concerned with up to around 6.5 gear ratios which will get you to 65 mph in a jiffy. So with the 727, you get the equivalent of THREE gears to 60, ending at 6.08.. Whereas
with the 5-speed you get TWO ratios, ending at 6.10.
Guess which combo will be quicker to 60 ...... without tirespin.
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Looking to the Eighth, we see 3.55s to the auto, versus 4.13s to the 5-speed; not enough to catch up.
Looking to the Quarter we see that neither has appropriate gears, but the stick car might have an edge, if it catches up early enough.
You said
"without swapping anything else."
IMO this is a mistake.
The 5-speed wants deeper gears, and then it just may out-perform the auto car.
Lets say you regear the 5 speed and let's say you do it with the .81 overdrive. this will then allow 3.91s; so lets recalculate the roadgears. I get
11.22-7.39- .500- 3.91-3.17od final drive. Now lets compare that to the auto
14.34>11.80-6.08-3.55-(3.23 cruize with a loc-up)
Tuff call who wins, but if I had to bet, I would still bet on the auto.
Save your cash, install a hi-stall.
Already got one?
then install a supercharger.
You just like shifting?
Then install a manual VB and a floor shifter.
What a Mopar streeter really needs, IMO, is an A518./hi-stall/loc-up, and something like 4.30s. Here are those gears;
2.45-1.45-1.00-.69 and in roadgears with 4.30s, adjusted as before;
18.96>13.68-8.10-5.16-3.26-2.97 in loc-up........ or, with 3.55s
15.65>11.29-6.68-4.26-2.67-2.45 in loc-up ........... Yeah, I'm liking that one.
Or solve all your problems with a supercharger, the regular TF, and something like 2.76 gears. If the super adds 50% to your low-rpm torque, it will feel like the 3.23s are 4.85s, and so
2.45-1.45-1.00s would, in roadgears, feel like
21.37>16.61-9.83-5.33- all at WOT, going to 3.39 at cruize. Those numbers are so big, you could run 2.76rear gears, for
18.25>14.2-8.40-4.97 all at WOT, going to 2.90 at cruize
Or, you know, with a super, you can run ridiculously low rear gears.
But I gotta tell ya, if your current street-combo at WOT, is already spinning the tires all the way thru First gear, and half way thru Second; more power will not make your car any quicker to 60mph. Fix this first.