There are really 3 different methods and speeds of reading, but to truly understand everything that is written in it's entirety only the 1st method is recommended:
1...When you read and fully process everything that is written so it's understood in it's entirety.
2...When you consciously read every word in your head with only partial processing and understanding.
3...When you skim through without consciously reading every word with very limited processing and understanding.
Sometimes with practise people can get better at prioritising what is processed and understood when reading at speed 2 or 3 to gain the most understanding without truly processing everything 100%, this makes them better at speed reading.
Personally I can read quite quickly and still hear all the words in my head up to about 600 and I can skim right up until the end, but if I want to truly understand and 100% process all the information properly I can only go up to around 200.
Note: I am definitely on the autistic spectrum, but unlike a high proportion of people here I'm NOT classed as having Asperger Syndrome and this may effect my results. This is because I was extremely slow developing speech and language as a young child, but unlike both my low functioning autistic brothers I started dramatically improving as I got older, although I've always kept numerous autistic traits (my now adult brothers can't read or write at all, in fact they also can't count or tell the time). Even as a teenager however I was the only person at school in the top group in mathematics and the remedial group in English (below the 3rd and usual bottom group for a small number of children requiring special help). The Internet has however greatly improved my reading further as an adult over the years since I first started using it from 1994. I was initially diagnosed as autistic along with both my brothers in the 1970s, but this was updated to
ASD and
OCD after a more recent re-diagnosis a couple of years ago (I think the 2nd diagnosis is a bit silly because OCD is part of ASD).