The problem with more stall is that, as with many things, there's a right way to get more and a wrong way. There's a compromise too.
With a converter of a given size (e.g. 12", 11.25", 10.5", 9.25" etc.) there's a sort of "stall butter zone" or range of stall speeds that can be obtained by varying the design of the impeller, pump and stator. Stall speed (range) and converter size are inversely proportional - that is to say a larger converter will have a lower range of obtainable stall speeds.
The problem is that early on, many converter manufacturers weren't making converters using their own designs or parts - they would simply assemble the converters using parts from other companies. There were some who would, for example, buy an off-the-shelf Ford 11.25" converter, cut it open and tweak the insides a bit to increase the stall then turn around and sell it as a 2800 or 3000 stall converter for 5x what it cost them to buy. But it would be a completely different animal compared to a 10.5" 3000 stall converter on the street. Even with the larger diameter, it would have a much more "sluggish" feel to it because its stall was raised to the upper limit of what the size could physically support.
The problem with doing that is not so much that the stall itself isn't as advertised, but comes more from the fact that when you raise the stall of a given converter size close to its upper limit, you also reduce the torque multiplication coefficient (K-factor, as Ford calls it) and lose the low-RPM torque transfer function. At low speeds the fluid just cavitates and doesn't really transfer any torque. You need to spin it much faster to get any action through it.
The fix to that is to get a converter that's properly sized for the stall speed. When you reduce the size of the converter, without changing the design of the insides, the stall naturally increases but you don't change the torque multiplication coefficient as dramatically. That means that at 7 or 800 RPM, you still get enough torque through the converter to cause the car to roll forward, or keep it from rolling backwards down hills when you take your foot of the brake. 12" converters are happiest to stall around 1600-1800. 11.25s are happy around 2400. 10.5s seem to be happy around 3200, and the 9s are up around 3800 or more. When you properly shrink the converter to get more stall, you don't lose the "creep factor" as much.
All that doesn't mean there's no difference in how the car feels. It absolutely feels "looser" when the converter is unlocked, but a properly designed and sized converter will definitely
not simply spin up to the stall speed before the car starts moving. In my case, most of the time the engine will spin up to about 2000 then eventually get to around 2500 RPM before it shifts as I drive normally and keep up with traffic. To improve the feel at speed I also lock the converter once in 2nd gear and above about 12 MPH.
This is the tug-of-war that's played when selecting a converter for any kind of build. Higher stall lets you get the car into the powerband right away, regardless of the speed of the vehicle, but most people don't drive their cars on the streets the way they would at the track. There's that often overlooked or undiscussed gray area of "what happens when you're driving in town with a 4200 stall converter?". This is why I went with a relatively large diameter, modestly-spec'd converter; I own my car to drive it (on the streets), not race it.
