I have two 20 gallon tubs next to each other, well 3' apart. In one I transplanted one plant. In the other I transplanted two at opposite ends of the tub. The three plants are not genetically identical but very close, they all came from the same parent plant and one shows a difference in dominant genes but all were growing at the same rate.
The plant alone in the tub is shorter, presumably not having to compete as much for light, but has about 20% more peppers on it as each individual plant in the two plant tub. I expect this % to increase because the plants in the two plant tub are shading each other more and more with each passing day.
To put it in perspective, the lone plant has close to 400 peppers large enough to count on and the two sharing a tub, over 600 and soon to grow double what the last node split did. My take on this is that if you have a limited grow area, more plants per that area can catch more sun earlier in the season, but that ultimately if you can devote a larger grow area you are better off using more pots to do so. If you get the soil and nutes right, what remains is how much sun they catch. The longer your season and the larger the plants grow, the more having them in close proximity causes a slowdown in growth rate and yield by reducing the solar energy they collect.
On the other hand if you have a short season, get as many light catching leaves out there as you can early though even then, if they are in separate pots you can spread them out as they grow.