Still the Flops metric clearly shows that while in this generation consoles got GPUs that was on the same level or even faster in Flops than the best PC GPUs of the same time, in the next generation this isn't so - PS4 got the GPU which has two times less Flops than even Tahiti.
You may do whatever perf/watt comparisons you want but 680/7970 cost exactly the same now as X1800/7800GTX did back then (actually, their prices was even higher than 7970 and 680 cost now) - and that's the only metric that matters when you compare two products in retail. Current PC GPUs draw much more power than R520/G70 did, sure, but who cares? It's the result per dollar - the Flops, the fps, resolutions, shader complexity - that matter.
As for the Titan not being 2.5x as fast as Pitcairn (which is actually faster than PS4 GPU) have a look at this for example:
I'm not saying that this is an indication of how they compare going just from their Flops number, but this proves that Titan can indeed be 2.5x faster than Pitcairn/7870. And that's something that simply wasn't the case between G70 and RSX or R520 and Xenos.