This is great information and thanks. I surely forgot about the 5a ports. So, I would probably use a separate power supply with a dist. board to power the pixels while the data comes from the ports?Somewhat indirectly you answered one of your own questions. If you already know 500 pixels at 80% will require approximately 22 Amp, then to find how to run them from a single port you only need to know what amperage the controller port is capable of. From that calculate backwards to determine the pixel maximum drive level. As this thread began with a Falcon F16v3/F4v3, (ports fused at 5 amp) it is an approximate 16% drive level for 500 pixels at the usual .055/.06 Amp per WS2811 pixel.
A similar manner can be used to determine the maximum pixels per port without power injection. WS2811 pixels driven at 80% would be about 105 pixels. If the drive level would be decreased to 30% then about 275 pixels.
Asking if a 350 Watt supply will run the pixels is a apples to oranges question. Amperage is a defined quantity while wattage is calculated. Is 6 watt 2 Amp at 3 Volt or 3 Amp at 2 Volt or 1 Amp at 6 Volt; somewhat iffy isn't it? So, without knowing more about the supply one cannot accurately answer the question. From the other information you posted it seems you are asking about a Meanwell LRS-350-5 or a -12 supply so yes, either a 5 Volt or 12 Volt 350 Watt supply will drive the pixels. Without power injection, not at 22 Amp however. The limitation is not the supply but rather the AWG wire used in the string. At some length or number of pixels depending upon drive level, pixel type, and AWG size, a tradeoff will be reached. The end pixels cannot illuminate and/or amperage in the first part of the string is above AWG amperage capacity and is either heating the wire or causing a high voltage drop inhibiting string operation or both.
So, split the strings? Strategic power injection is better in my opinion. So far, like i13 I do not power any pixels through the controller and like Dan, prefer the F4 over the F16.