Couldn't find the other thread to post this in. So here it is. HardOCP overclocked the 290X to the max and compared it to the 780ti reference OC'ed to the max. Do note. Reference 780ti. Not a fair comparison because the 780ti is reference and the 290X is an aftermarket card with a custom PCB.
XFX R9 290X Double Dissipation Edition CrossFire Review - Take two custom XFX R9 290X Double Dissipation Edition video cards, enable CrossFire, and let your jaw hit the floor. We will test this combination against the competition in a triple-display Eyefinity setup as well as 4K Ultra HD display gaming. We will find out if custom cards hold any advantage over the reference designed R9 290X.
The folks at techPowerUP have posted a thirty page review of the MSI R9 290X Lightning 4GB. If I were you, I'd pack a snack before clicking the link. ;)
The $700 MSI R9 290X Lightning is MSI's latest flagship card geared toward overclockers and enthusiasts. It comes with a large overclock out of the box, higher than any other custom R9 290X available today.