there are so many variables, it's impossible to generalize. Best you can hope for is to compare one particular brand of old card with a new one, playing exactly the same game with the same settings.
eg. I could barely play any recent game with my old 8600GT and it's tiny fan emitted an annoying noise. A year ago, I got a HD7750, which used the same power, but had 9 times better performance and was a little quieter due to its slightly larger heatsink and fan, but still quite annoying when pushed and most games were limited to low settings. Now I have the R9-290 with the Sapphire Tri-x cooler. I can play almost everything on max with 3 monitors, yet I can barely hear its triple fans. If it was the AMD reference design, it would be a lot noisier. So how is it possible to compare?
What's clear is, top end GPUs offer many times more performance than the top end GPUs of several years ago, yet the power consumption (and hence heat produced) has not risen proportionately with performance. This is mainly due to die shrinking of the silicon and optimization of the architecture, which means they require less power to do more. Heat sinks have become more efficient and larger to cope with the massive increase in performance, despite the technological improvements.