You might be surprised, "older single-core games" like Crysis and Skyrim really do not run all that well even with "modern" architectures behind them. And in particular they often do quite poorly with AMD due to latency issues.

Per-thread performance really hasn't improved all that much since the days of, say, a 4.7 GHz 2600K. Core counts have gone up drastically, but that doesn't help your single-threaded game from 2007.