The 1750 MHz timing strap mod is only for cards with Samsung memory. I have a Nitro+ RX 570 4GB card with Hynix memory. I copied the 1500 MHz strap to the higher timings and get ~29 MH/s UBQ and 760 MH/s DCR dual mining. I use an overclock of 1150 MHz core clock 2075 MHz memory clock with a -96 mv undervolt and -10% power limit in Afterburner.
Hum... I tried flashing 1500 strap to the higher timings (even 2250) but when I OC my mem to 2000 on AB, the system crashes. Don't think it worked :S
If your cards has two sets of memory timings you need to copy the 1500 MHz timing from both sets. Use 1:1500 strap to replace all the higher frequency 1: straps and the 2:1500 to all the 2: higher frequency straps.