[DELL R730XD vs custom build]

I would say B for future upgradability, maybe? Also, dedicated gpu for plex is overkill in my opinion. igpu works great.

 

Downsides, no ECC...maybe?

[Plex Hardware Recommendations]

Just thought I would post my setup that currently runs great for Plex.

 

Intel i7 13700k - Overkill for plex - just make sure yours has igpu for transcoding.

ASUS PRIME Z690-A

128gb DDR5

Synology NAS - 20 terabytes - with 10gigabit over fiber. Stores all TV/Movie media

 

The Synology and Unraid server are in different locations (house/detached garage) and serve as duplication for most data and backups.

If you will only be running plex you don't need latest CPU, mb, etc. 

 

Hope it helps.