Intel Core 2 Extreme QX9775 EU80574XL088N (BX80574QX9775 / BX80574QX9775A)

Core 2 Extreme QX9775 microprocessor, part of "Skulltrail" platform, was launched in February 2008. "Skulltrail", that also included desktop D5400XS motherboard, was demonstrated numerous times before the official launch, and was positioned as a gaming and digital media platform. The platform was unique in a sense that it took "Extreme" from the family name to the extreme. While frequency and features of the QX9775 processor were not different from the QX9770, the QX9775 supported dual CPU configuration. Being the socket 771 CPU, the QX9775 couldn't work in consumer socket 775 motherboards, and required quite expensive dual-socket D5400XS board. The board also accepted up to four PCI Express graphics cards, either NVIDIA SLI or ATI CrossFireX, and supported up to 8 GB FBDIMM 800 memory. Although the board had sockets 771, it used socket 775 heatsinks. The price for this platform was also "extreme". Each QX9775 processor had suggested retail price $1499, and the price of the D5400XS board was $600+, so the total just for two CPUs with the board would be more than $3600.

The QX9775 platform outperformed QX9770 by large margin in multi-threaded digital media applications, but it didn't always have the best performance in games owing to their poor utilization of multiple cores. Compared with the QX9770, the platform had noticeable performance advantage in some games, while not showing any performance difference in other games, or, in some cases, showing worse performance due to lower memory bandwidth than the memory bandwidth available on QX9770 consumer boards with DDR3 memory.