For our manual overclocking tests, we used MSI Afterburner. Our best results are as below.
Interestingly, Acer has restricted the power limit for the 4090, in that it cannot be increased over 100% (450W). Our best result came with an extra 205MHz added to the core, and 1475MHz added to the memory.
Older data is represented by the greyed-out bars on the above chart.
This saw our real-world clock speed increase by almost 170MHz, now averaging 2810MHz over our thirty minute stress test.
This overclock didn't net us particularly inspiring gains, with just an extra 2-6% performance on offer in the three titles we re-tested, hardly worth doing.