What GPU is in this build and what is its boosted clock speed?

GPU is the Gigabyte Aorus Master Ice 5090. Boosted clock speed is 2655 MHz.

What is the brand of this mother board and what is the name of the mother board model, also does it have PCIe 5.0?

The brand of the motherboard is AORUS and the model name is X870E AORUS Mother Board. It does not have PCIe 5.0; it supports PCIe 4.0 and PCIe 3.0.

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GIGABYTE AORUS SUPREME 5 ICE Gaming Desktop PC, AMD Ryzen 7 9800X3D, AORUS RTX 5090, 64GB DDR5 RAM, 2TB Gen5 NVMe SSD, Windows 11 Home, White

AORUS Design Lab - Sharp yet sleek mid-tower case equipped with a tempered glass side panel.
SUPREME Performance, Always Ready - Game, create, and stream with a AMD Ryzen 7 9800X3D Processor, AORUS RTX 5090 Graphics Card, ultra-fast 64GB DDR5, 2TB Gen5 SSD, and WiFi 7.
All-Round Cooling - Keep your system cool with a 360mm AORUS AIO liquid cooler and our signature WINDFORCE cooling system featuring innovative Hawk Fans configured for optimal airflow path.
RGB Fusion 2.0 - With GIGABYTE Control Center (GCC), customize and sync lighting modules to create a custom battlestation that's uniquely yours.
Maxxed Out Settings - Play all your favorite games and the latest AAA titles at max quality and ultra-high frame rates.