Cryptonight - Core or Memory Heavy?

[smoolae]

I have my R9 290s mining Electroneum atm with 1100 core / 1250 memory and hashrate is 719 H/s per card.
Whenever I touch either one of the clocks (lower/rise), the hashrate gets affected (in a bad way).

So I'm left wondering, which one of them is actually "the bigger player" with Cryptonight?

Also, should I use AMD's Blockchain drivers with Cryptonight (right now I'm using Crimson 15.12)?