M2 with it for PMS and nzb file downloads?

[Enquiries]

Just picked up a used DS920+ to move from my DAS. It will be used for Plex Server and library storage, using SABnzbd or NZBGet incorporating SONARR and RADARR. Should I invest in M2 cards for cache or pooling to increase download efficiency and speed, I am on a 1Gbps line.

Or should I invest that money in larger capacity HDD? I have RAM in hand to install once I receive the unit. Thanks for the help.