Being single-threaded is why the original Crysis is hard on computers now(!!). When Crysis was being developed people still thought 5-10Ghz was coming Any Day Now.
2007 was well into Intel Core territory, Intel had given up on clockspeed-at-all-costs Pentium 4 Netburst, so it was generally accepted that clocks weren't going to keep up as fast as before.
Even if Crytek took a year off developing new games after the release of Far Cry, that still puts the start of Crysis development before the announcement of Core (early 2005 IIRC).
You might could hit 5Ghz by overclocking the appropriate CPU. I remember 10 years ago looking at the liquid cooling setups needed to hit 5Ghz on a core.
My 12400F boosts to 5GHz for the majority of each day. It's literally normal for me. I've gotten it to almost 5.3GHz before, but it's not really stable above 5.2GHz.
