WD Gold is Enterprise Class but geared towards the channel sales. For large project and implementations, Ultrastar is more suitable becuase of following reasons
1. Ultrastar Is Available in SAS and SATA. Gold is available only in SATA
2. Ultastar can be ordred in 512e, 512n ( in lower caps) and 4Kn . Gold format is fixed and can't be changed ( 512n/512e)
3. Ultrastar Can be had in TCG, SE, FIPS encryptions unlike Gold.