I see a lot of people around here trying to get help to hit Hashrate "xx" on card "RX 4yy". No. Not how the silicon lottery works.
The memory used on these cards (especially the 480 8GB reference cards, which is what I use) varies WILDLY in memory performance.
When you first get the card, copy 1750 timings into 2000, and then boot up your miner. Set the core clock at 1175MHz and leave voltage for now (1175MHz seems to be enough to keep the memory controller fed). Increment the memory clock in steps of 25 MHz until you see hashrate start to decrease (or it might just straight up crash). Fine tune using increments of 5 or 10 MHz, and then save it. If you want to try be brave, you can copy 1625 timings into 2000 and repeat.
The only reason why you would move to a lower memory timing strap is if your memory is severly clockspeed bound. Here's a personal example:
I have 3 8GB reference RX 480s. Blower cooler (thermal paste changed to MX-2). All have their core clock set to 1175 MHz. Fan speed set to 2920/3500. Power at +50
One card does 2250 MHz Memory at 1750 straps- 31.3 MH/s (i fuckin love this card)
One card card does 2075 MHz memory at 1750 straps- 28.8 MH/s (this one's shit) [2045 MHz at 1625 strap- 28.2 MH/s]
One card does 2175 MHz memory at 1750 straps- 30.3 MH/s. (meh)
Yes, for the shit card I tried pasting 1625 timings in. The max performance WAS lower than the 1750 timings. I can't get the card over 29 MH/s unless I try custom timings or something. Theres nothing I can do about it. Oh well.
As long as you are getting near the average hashrate, youre good. No need to be confused anymore.