It´s a stress test level. And it isnt designed for outdoor levels, therefor it doesn´t use LOD like other games with outdoor scenery. And yes it´s not the fastest engine out there, especially compared to "modern games", guess you mean AAA releases.
If you want to measure the speed it gains with an average level design then try the previous demo Number 7.
If you want to measure the speed it gains with an average level design then try the previous demo Number 7.