Because the PS2 is using regular DVDs with ISO fle system, they are also using the regular DVD error correction and recognition system. So there is no reason to slow down the reading process, your DVD drive will report reading errors to you at any speed. Just in case there are reading error, you can try to read the media with a very slow speed to increase reading accuracy and sometimes you can rescue media with this.
Slim PS2 SCPH-70004 (v13) w/ FMCB, 3x Sony 8MB, 1x MaxMemory 16MB (Backup card)
I'm not available for FMCB installation service until I can guarantee a processing time of a few days again, sorry.