You can run 1200 pixels with no issue depending In two things.
- the refresh rate.
- If the software allows it.
If I remember correctly wled has a limit of something like 8 universes which is 8 * 170 pixels. The hardware is not technically limited in many cases. My example of what I mean by that statement is: if you Had a supercomputer it no matter how hard you try could not run more than around 800 pixels with a 40 FPS refresh rate. This is due to the clock speed of the pixel, the super computer is clearly fast enough.
When looking at a single output. Changing hardware from a d1mini to a teensy, pi, or beagle bone really only changes things minimally. This a because Most of the limit on number of pixels has to do with refresh rate of the pixel itself vs the hardware it’s tied to. However changing the driving hardware can allow for multiple outputs vs one output. Wired Ethernet vs wireless, etc.
Conclusion if you want to drive 1200 pixels I would either get a falcon picap or similar, or buy two art sticks. The picaps support two outputs so you could put 600 on each. The guy who makes the art stock sells one as well as falcon.