I have an answer for you on that - at 1080p, Crysis 3 is largely CPU-bottlenecked, even with a big CPU overclock and 8 threads. In other words, at 1080p, it's not a good GPU benchmark - I should have mentioned that.
Now, what's very interesting is that despite this, the R9 290 runs faster than the GTX 780, which suggests that it may present a lower driver overhead to the CPU. I have another CPU-bottlenecked game, Hitman, that shows similar, surprising results.
I'm pretty confident that my memory frequency is producing positive results based on trying a number of settings - you do need to be careful, however, with VRAM overclocking, because you can continue to increase clocks only to get negative scaling.
One last tidbit: you mention that the Tri-X overclock looks pretty easy to achieve. I immediately set my clock to 1100MHz based on all the reviews I'd read using manufacturer samples. No go. Needed extra voltage. Take the OCs using reviewer samples with a grain of salt. Based on actual user reviews, I don't think going over 1100MHz without a significant voltage increase is going to be likely. I can hit 1075MHz stable without voltage, and that's where I'll actually use it, because temp/power is so much lower.
