We aren't going to see ludicrously high clock rates for the foreseeable future. There are a lot of compounding factors as to why, but the biggest ones are the pressure for efficiency driving designs that aren't dumping higher and higher voltage to get frequency, the diminishing returns on voltage vs frequency (see Ryzen, where a 20% improvement in clocks costs about a 50% increase in power draw across all skews, and similar situations happen with Intel).
That being said, a 4ghz Skylake core crushes a 4ghz Core 2 core. Depending on your benchmark used it can perform anywhere from 80% to upwards of 170% faster per clock. You don't get as dramatic year over year improvements increasing the the per cycle performance, but innovations leading up to ~2004 (or 06 for the multicore boon) were just stuffing power hungrier and hotter transistors on smaller dies.