Increase in the core speed doesn't have much effect in xmr mining.
i usually drop it a lot on ETH. I was asking because i'm using the same modded bios for XMR. For example, i've a RX460 doing 13.5MH on ETH (dualmining dcri 23) with core 1000 and mem 1950. The same gpu does around 400h/s on XMR. Not sure if i can improve it by increasing core speed.