Thanks both Gorosden and batsonxl for replying!
Yes of course it's not RTX 2700, but RTX 2070. My mistake, sorry.

I tried your settings:

> core clock: -502, memory clock: +750, power limit: 60%
> system crashed (I think because memory clock was too high)

> core clock: -502, memory clock: +0, power limit: 100%
> nothing significant happens: core clock stuck @300MHz, memory clock @7000MHz and hashrate @9MH/s

> core clock: +1100, memory clock: +0, power limit: 100%
> same as before: core clock stuck @300MHz, memory clock @7000MHz and hashrate @9MH/s

In order to get core clock work properly I'm forced to set power limit over 100%