I wanted to update that I seemed to be incorrect in stating that the DLNA Client Preferences were not updating. On my one client I have the following listed:
IP=10.10.10.95,DirectPlay=false,DirectStream=false,LocalResolution=320x240,RemoteResolution=320x240,OnlineResolution=320x240,LocalVideoQuality=24,RemoteVideoQuality=24,OnlineVideoQuality=24,SubtitleSize=60,AudioBoost=100,MusicBitrate=192;
As you can see I turned everything down to lowest settings (and modified subtitle size). But these settings seem to make no effect. The video appears the same on the DLNA client and Plex dash still reports it is streaming at 1080p.