It's ~33% slower than Skylake/Kaby Lake, clock for clock, on average.
It still has a good amount of L3 cache, triple channel memory, and overclocking on it is pretty good. On average, it clocks around 4.5GHz.
The problem with it is basically you have no upgrade path, and it's on a pretty old platform.
The i7-980X clocked at 4.5GHz is going to perform around the same as a Ryzen 5 1600X clocked at 4.0GHz in gaming (maybe a little worse) on average, however, it's getting beaten in computing tasks, especially the ones that are optimized for throughput. Triple channel memory is going to help the 980X a bit in memory-sensitive applications, but it's on slower DDR3 memory. Keep in mind the i7-980X is going to consume more power as well.