Our temperature tests make it clear that overclocking the reference Radeon R9 290X in the automatic fan regulation mode is pointless as the clock rate would just drop down as soon as the GPU temperature hit 94°C. That's why we fixed the fan speed at 65% or 3660 RPM and didn't increase the core voltage. We managed to increase the GPU and memory clock rates by 130 and 760 MHz, respectively.
The resulting clock rates were 1130/5760 MHz:
The fan worked at 65% of its full speed and roared mercilessly, yet the GPU was as hot as 90°C.
Even though we achieved some success in our overclocking experiment, we have to admit that the reference Radeon R9 290X is no good for overclocking unless you are completely deaf.