A 3U really opens things up for possibilities: - Full-height PCI cards fit (though some GPUs have taller than full-height coolers; if the HS/F protrudes above

A 3U really opens things up for possibilities: - Full-height PCI cards fit (though some GPUs have taller than full-height coolers; if the HS/F protrudes above the mounting bracket, you'll have to measure). - You can use larger fans, which can help a lot with airflow and/or noise. Just throw away the fans that come with the case as anything designed for a rack assumes you'll be wearing hearing protection while working around it. - More motherboard options. If you use a power-supply designed for rack-mount, standard ATX motherboards fit fine. If you want to use a desktop power supply there are plenty of micro-ATX options.