The Mac Silver Tower 4,1 and 5,1 remain one of the most powerful Macs ever made, depending on your processor. Even the eight core 2.26 GHz version is incredibly powerful and fast, outrunning any MacBook Pro and most iMacs, as will a hexacore 3.33 GHz or 3.46 GHz. Certainly they are more expandable, repairable and upgradeable than any other Mac built since, with SATA SSD and PCI cards and graphic card upgrades readily available and easily installed. For video editors, the Mac Pro Silver Tower is one of the best computers ever built.
In terms of cost for performance, no current Mac whether iMac or iMac Pro can touch the 4,1 and 5,1 Silver Towers. What's especially wonderful is that both of them will still run the latest Apple OS and software perfectly, with just a bit of preparation. I'll take you through the steps of a successful deployment of a 4,1 Silver Tower with High Sierra.
Start by Testing Your Hardware: Apple Hardware Test
The first thing you should do is test your hardware. This is easier said than done on older hardware. Apple has some lovely software called Apple Hardware Test a.k.a. as AHT. There's no joy in suffering through crashes which are hardware related, trying to debug your OS (software).
Normally you find AHT at this path
Unfortunately, recent versions of the OS have not included AHT or at least not for older computers. Happily some enterprising Apple fans have collected all the versions of AHT out there for all kinds of Apple computers including Powermac, Powerbook, iBook, iMac, MacMini, MacPro, MacBook and MacBooks Pro.