Cactus grows faster with more chunks rendered?
This is a case of randomness. Rebuild your exact farm in a creative world, but much bigger. Then download carpet mod and tickwarp the game to see If it has any impact. I would tickwarp for about a week or so to get a good test. (Tickwarping is a plugin that makes the game faster, so you can run a farm and get the rates of a week in an hour)
I believe that the chunks rendered will have no impact on the farm
Also having it in the distance might make it in the lazy chunks, which is a whole new topic that's hard to explain here.