Is it worth trying to stop subvocalising and learn various "Speedreading" techniques for when I'm just reading for fun and not for a test? Basically does speedreading take the fun out of it?
Depends if you just want the plot forcefed to you by a conveyor belt or not, you won't chew and appreciate the flavour is my take on it.
Maybe this is a bit far, but for me the experience was akin to reading a chapter summary I found online, I only remembered the neat and obvious.
Reading very fast is just for absorbing information, you won't consider anything deeply or enjoy it.
Still, I used to read like 20 pages an hour, it was impossible for me to complete books. Practicing speed reading helped me move to the standard.
You can stop subvocalizing and not speedread. Not subvocalizing is a part of speedreading, but it's not the exact same thing. Speedreading is literally about skimming well, which is why it's only good for work or school where you just want important bits of info out of a text so you can save time.
Reading without subvocalizing is just a habit some people have. You can read without subvocalizing and take your time with a book and have an overall engaging experience. You can still have a good memory of the text and savour the prose. People who tell you otherwise are just bad at reading without subvocalizing.
Harold Bloom is someone who reads at a really fast rate, but he still recommends things like thinking deeply about what you're reading, rereading to gain better understanding of the book, and going slow at the right moments.